MESOSCALE APPLICATIONS

Anderson, C. J., R. W. Arritt, J. S. Kain, 2007: An alternative mass flux profile in the Kain-Fritsch convective parameterization and its effect on seasonal precipitation.. J. Hydrometeor, 8, 1128-1140.

Baldwin, M. E., S. Lakshmivarahan, J. S. Kain, 2005: Development of an automated classification procedure for rainfall systems. Monthly Weather Review, 133, 844-862.

Baldwin, M. E., J. S. Kain, 2006: Sensitivity of Several Performance Measures to Displacement Error, Bias, and Event Frequency. Weather and Forecasting, 21, 636-648.

The sensitivity of various accuracy measures to displacement error, bias, and event frequency is analyzed for a simple hypothetical forecasting situation. Each measure is found to be sensitive to displacement error and bias, but probability of detection and threat score do not change as a function of event frequency. On the other hand, equitable threat score, true skill statistic, and odds ratio skill score behave differently with changing event frequency. A newly devised measure, here called the bias-adjusted threat score, does not change with varying event frequency and is reletively insensitive to bias. Numerous plots are presented to allow users of these accuracy measures to make quantitative estimates of sensitivities that are relevant to their particular application.

Available online at ://http://available soon from AMS.

Brooks, H. E., 2006: A global view of severe thunderstorms: Estimating the current distribution and possible future changes. Preprints, Symposium on the Challenges of Severe Convective Storms, Atlanta, GA, USA, American Meteorological Society, CD-ROM, J4.2.

Brooks, H. E., A. R. Anderson, K. Riemann, I. Ebbers, H. Flachs, 2007: Climatological aspects of convective parameters from the NCAR/NCEP reanalysis. Atmospheric Research, 83, 294-305.

Annual cycles of convectively important atmospheric parameters have been computed for a variety of from the National Center for Atmospheric Research (NCAR)/National Centers for Environmental Prediction (NCEP) global reanalysis, using 7 years of reanalysis data. Regions in the central United States show stronger seasonality in combinations of thermodynamic parameters than found elsewhere in North America or Europe. As a result, there is a period of time in spring and early summer when climatological mean conditions are supportive of severe thunderstorms.
The annual cycles help in understanding the large-scale processes that lead to the combination of atmospheric ingredients necessary for strong convection. This, in turn, lays groundwork for possible changes in distribution of the environments associated with possible global climate change.

Available online at ://http://www.nssl.noaa.gov/users/brooks/public_html/papers/ECSS2004.pdf.

Brooks, H. E., 2007: Development and use of climatologies of convective weather. Atmospheic Convection: Research and Operational Forecasting Aspects, D. B. Gaiotti, R. Steinacker, F. Stel, Ed(s)., SpringerWienNew York, 123-132.

Estimates of the occurrence (“climatologies”) of convective phenomena in time, space, and intensity can be useful in a variety of contexts. They provide background for forecasters, and the risk management and meteorological research communities. In part, because of the different needs of those user groups, caution must be applied when developing and using climatologies, especially if the intended application is outside of the original intent of the developers.

Brooks, H. E., 2007: Environmental conditions associated with convective phenomena: Proximity soundings. Atmospheic Convection: Research and Operational Forecasting Aspects, D. B. Gaiotti, R. Steinacker, F. Stel, Ed(s)., SpringerWeinNewYork, 113-122.

An important tool in understanding the relationship between environments and observed severe thunderstorm events are vertical profiles of environmental conditions collected in the vicinity of the storms. These relationships can help in the future forecasting of weather. In this paper, the use and cautions associated with these so-called proximity soundings are discussed.

Brooks, H. E., 2007: Ingredients-based forecasting. Atmospheric Convection: Research and Operational Forecasting Aspects, D. B. Gaiotti, R. Steinacker, Ed(s)., SpringerWienNew York, 133-140.

Forecasting the weather can be thought of as a problem in extracting a small signal from a noisy background field. Much information is available to the forecaster, but, frequently, only a small amount of that information is of importance for solving the forecast problem(s) of the day. As a result, an approach to forecasting must maximize the efficiency of the process. An effective way, particularly for hazardous weather, is to identify the ingredients required to produce a particular weather event and then to focus on the processes that can affect the presence of those ingredients. This allows the forecaster to narrow the range of aspects of the observations and model guidance that are considered during the forecast shift and, it is hoped, identify crucial developments as they occur.

Brooks, H. E., 2007: Practical Aspects of Forecasting Severe Convection in the United States: Environmental Conditions and Initiation. Atmospheic Convection: Research and Operational Forecasting Aspects, D. B. Gaiotti, R. Steinacker, F. Stel, Ed(s)., SpringerWienNew York, 141-148.

The first stage of forecasting convective weather involves forecasting the evolution of conditions that are favorable for the development of storms and their probable initiation. The scale of the forecasts are typically on the order of 100 km or larger and the lead time between the forecast and storms is 1-48 hours. In the United States, procedures have evolved so that the Storm Prediction Center of the National Weather Service has the responsibility for issuing these forecasts for the contiguous 48 states (the part of the US excluding Alaska and Hawaii.)

Brooks, H. E., 2007: Practical Aspects of Forecasting Severe Convection in the United States: Storm Evolution and Warning. Atmospheic Convection: Research and Operational Forecasting Aspects, D. B. Gaiotti, R. Steinacker, F. Stel, Ed(s)., SpringerWienNew York, 149-156.

In order to protect life and property, forecasts of severe convection are critical on short time and space scales (on the order of 1 hour or less and a few 10s of km or less). Accurate assessment of the environment and monitoring of high-resolution observational data, frequently focusing on radar-observed evolution, are essential in this process. In the United States, these short-term time and space scale forecasts are referred to as warnings and are prepared by local forecast offices of the National Weather Service, who have responsibility for forecasters on the order of 100,000 km2.

Brooks, H. E., C. A. Doswell III, D. Sutter, 2008: Low-Level Winds in Tornadoes and Potential Catastrophic Tornado Impacts in Urban Areas. Bulletin of the American Meteorological Society, 89, 87-90.

Brooks, H. E., N. Dotzek, 2008: The spatial distribution of severe convective storms and an analysis of their secular changes. Climate Extremes and Society, H. F. Diaz, Ed(s)., Cambridge University Press, 35-54.

Severe convective storms are responsible for billions of US dollars in damage each year around the world. They form an important part of the climate system by redistributing heat, moisture, and trace gases, as well as producing large quantities of precipitation.

Reporting of severe convection varies from country to country, however, so that determining their distribution from the reports alone is difficult, at best. Evidence does exist that the intensity of some events, particularly tornadoes, follows similar distributions in different locations, making it possible to build statistical models of occurrence. Remotely-sensed observations provide some insight, but the relationship between the observable parameters and the actual events of interest limits the quality of the estimate. Another approach is to use observations of the larger-scale environments.

As has been stated, the relationship between the observation and the event limits the estimate, but global coverage is possible. Time series of the favorable environments can also be developed from such data. In order to improve the estimates, the most pressing need is better observational data of events. Very few countries have formal systems for collection of severe thunderstorm reports. A new effort from a consortium of researchers in Europe to develop a continental-wide database offers the possibility of a significant improvement in data in that part of the world.

Brooks, H. E., 2008: Extreme Weather: Understanding the Science of Hurricanes, Tornadoes, Floods, Heat Waves, Snow Storms, Global Warming and Other Atmospheric Disturbances. EOS, Transactions American Geophysical Union, 89, 258-258.

Extreme weather is of importance because of the threats it makes to life and property. At the same time, extreme weather is a great fascination for meteorologists as well as for the general public. The conditions and processes that lead to extreme weather—although governed by the same physical principles as “ordinary” weather—frequently are far from the average state of the atmosphere. Thus, explaining them in simple terms can be difficult. This book represents an effort to explain the development of extreme weather to the public.

Brooks, H. E., 2009: Proximity soundings for severe convection for Europe and the United States from reanalysis data. Atmospheric Research, 93, 546-553.

Proximity soundings from reanalysis data have been created for significant severe thunderstorms in the United States and Europe, along with corresponding soundings not associated with severe thunderstorms. The probability of a combination of convective available potential energy (CAPE) and deep tropospheric wind shear being associated with significant severe thunderstorms has been calculated for both areas. Probabilities of significant severe storms are higher for high CAPE and shear in Europe, but those large scale environmental conditions are experienced much more frequently in the US, so that the overall number of events is much higher in the US. Probabilities of significant storms are approximately constant for constant values of CAPElow asteriskShear for each of the datasets. High values of 0–1 km wind shear and low lifted condensation levels are associated with higher probabilities that significant severe thunderstorms will be associated with significant tornadoes.

A subset of the US data, taken from the southeastern US in the cool season, produces probabilities that are much closer to the European values than the overall US data. The environments also are closer to European values with relatively low CAPE and low lifted condensation levels. From the southeastern US data, it is shown that the probability of severe convection occurring with moderate values of CAPElow asteriskShear is much higher in the cool season than in the warm season. It is suggested that the higher probabilities result from stronger synoptic forcing and stronger and more frequent boundaries to initiate convection.

Bukovsky, M. S., J. S. Kain, M. E. Baldwin, 2005: Bowing convective systems in a popular operational model: Are they for real. Preprints, 21st Conference on Weather Analysis and Forecasting/17th Conference on Numerical Weather Prediction, Washington, DC, USA, American Meteorological Society, 2A.1.

Bukovsky, M. S., J. S. Kain, M. E. Baldwin, 2006: Bowing Convective Systems in a Popular Operational Model: Are They for Real?. Weather and Forecasting, 21, 307-324.

Bowing, propagating precipitation features that sometimes appear in NCEP's North American Mesoscale model (NAM; formerly called the Eta Model) forecasts are examined. These features are shown to be associated with an unusual convective heating profile generated by the Betts–Miller–Janji convective parameterization in certain environments. A key component of this profile is a deep layer of cooling in the lower to middle troposphere. This strong cooling tendency induces circulations that favor expansion of parameterized convective activity into nearby grid columns, which can lead to growing, self-perpetuating mesoscale systems under certain conditions. The propagation characteristics of these systems are examined and three contributing mechanisms of propagation are identified. These include a mesoscale downdraft induced by the deep lower-to-middle tropospheric cooling, a convectively induced buoyancy bore, and a boundary layer cold pool that is indirectly produced by the convective scheme in this environment. Each of these mechanisms destabilizes the adjacent atmosphere and decreases convective inhibition in nearby grid columns, promoting new convective development, expansion, and propagation of the larger system. These systems appear to show a poor correspondence with observations of bow echoes on time and space scales that are relevant for regional weather prediction, but they may provide important clues about the propagation mechanisms of real convective systems.

Case, J. L., S. R. Dembek, J. S. Kain, S. V. Kumar, T. Matsui, J. J. Shi, W. M. LaPenta, W. K. Tao, 2008: A sensitivity study of the operational NSSL WRF using unique NASA assets. Preprints, 9th Annual WRF Users' Workshop, Boulder, CO, USA, NCAR, P9.4.

Available online at ://http://www.mmm.ucar.edu/wrf/users/workshops/WS2008/abstracts/P9-04.pdf.

Cohen, A. E., M. C. Coniglio, S. F. Corfidi, S. J. Corfidi, 2006: Discrimination among non-severe, severe, and derecho-producing mesoscale convective system environments. Extended Abstracts, Severe Local Storms Symposium, 86th Amer. Meteor. Soc. Annual Meeting, Atlanta, GA, USA, American Meteorological Society, CD-ROM, P1.15. [Available from National Weather Center, 120 David L. Boren Blvd, Norman, OK, USA, 73071.]

Available online at ://http://ams.confex.com/ams/pdfpapers/103614.pdf.

Coniglio, M. C., H. E. Brooks, S. J. Weiss, 2005: Use of proximity sounding parameters to improve the prediction of MCS speed and demise. 21st Conference on Weather Analysis and Forecasting, Washington, DC, USA, American Meteorological Society, 3.3.

Coniglio, M. C., D. J. Stensrud, L. J. Wicker, 2006: Effects of upper-level shear on the structure and maintenance of strong quasi-linear mesoscale convective systems. Journal of the Atmospheric Sciences, 63, 1231-1252.

Recent observational studies have shown that strong midlatitude mesoscale convective systems (MCSs) tend to decay as they move into environments with less instability and smaller deep-layer vertical wind shear. These observed shear profiles that contain significant upper-level shear are often different from the shear profiles considered to be the most favorable for the maintenance of strong, long-lived convective systems in some past idealized simulations. Thus, to explore the role of upper-level shear in strong MCS environments, a set of two-dimensional (2D) simulations of density currents within a dry, statically neutral environment is used to quantify the dependence of lifting along an idealized cold pool on the upper-level shear. A set of three-dimensional (3D) simulations of MCSs is produced to gauge the effects of the upper-level shear in a more realistic framework.

Results from the 2D experiments show that the addition of upper-level shear to a wind profile with weak to moderate low-level shear increases the vertical displacement of parcels despite a decrease in the vertical velocity along the cold pool interface. Parcels that are elevated above the surface (1–2 km) overturn and are responsible for the deep lifting in the deep-shear environments, while the surface-based parcels typically are lifted through the cold pool region in a rearward-sloping path. This deep overturning helps to maintain the leading convection and greatly increases the size and total precipitation output of the convective systems in more complex 3D simulations, even in the presence of 3D structures. These results show that the shear profile throughout the entire troposphere must be considered to gain a more complete understanding of the structure and maintenance of strong midlatitude MCSs.

Coniglio, M. C., S. F. Corfidi, 2006: Forecasting the speed and maintenance of severe mesoscale convective systems. Extended Abstracts, Severe Local Storms Symposium at the 86th AMS annual meeting, Atlanta, GA, USA, American Meteorological Society, CD-ROM, P1.30. [Available from National Weather Center, 120 David L. Boren Blvd, Norman, OK, USA, 73071.]

Available online at ://http://ams.confex.com/ams/pdfpapers/104815.pdf.

Coniglio, M. C., H. E. Brooks, S. F. Corfidi, S. J. Weiss, 2007: Forecasting the Maintenance of Quasi-Linear Mesoscale Convective Systems. Weather and Forecasting, 22, 556-570.

The problem of forecasting the maintenance of mesoscale convective systems (MCSs) is investigated through an examination of observed proximity soundings. Furthermore, environmental variables that are statistically different between mature and weakening MCSs are input into a logistic regression procedure to develop probabilistic guidance on MCS maintenance, focusing on warm-season quasi-linear systems that persist for several hours.
Between the mature and weakening MCSs, shear vector magnitudes over very deep layers are the best discriminators among hundreds of kinematic and thermodynamic variables. An analysis of the shear profiles reveals that the shear component perpendicular to MCS motion (usually parallel to the leading line) accounts for much of this difference in low levels and the shear component parallel to MCS motion accounts for much of this difference in mid-to-upper levels. The lapse rates over a significant portion of the convective cloud layer, the convective available potential energy, and the deep-layer mean wind speed are also very good discriminators and collectively provide a high level of discrimination between the mature and dissipation soundings as revealed by linear discriminant analysis. Probabilistic equations developed from these variables used with short-term numerical model output show utility in forecasting the transition of an MCS with a solid line of 50+ dbZ echoes to a more disorganized system with unsteady changes in structure and propagation. This study shows that empirical forecast tools based on environmental relationships still have the potential to provide forecasters with improved information on the qualitative characteristics of MCS structure and longevity. This is especially important since the current and near-term value added by explicit numerical forecasts of convection is still uncertain.

Coniglio, M. C., D. C. Dowell, L. J. Wicker, 2007: Ensemble Kalman filter assimilation of Doppler radar data: Analyses of a developing MCS. Extended Abstracts, 22nd Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, American Meteorlogical Society, 3B.3. [Available from Michael Coniglio, NSSL/FRDD, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Recent efforts at the National Severe Storms Laboratory and the University of Oklahoma/Center for Analysis and Prediction of Storms have shown the positive impact of assimilating real Doppler velocity and reflectivity observations using an Ensemble Kalman Filter (EnKF) technique for the storm-scale analysis of supercell thunderstorms. Recently, the utility of this technique to other convective modes with multiple updrafts and more complex evolutions has been shown with analyses of the 16-17 June 2005 severe bow echo MCS across Oklahoma. It is well known that an accurate depiction of convective system cold pools is a prerequisite for the accurate short-term (1-12 h) prediction of MCSs by high-resolution numerical models. One of the most promising aspects of the analysis is the detailed and accurate depiction of the cold convective outflow and the robustness of the analyses to changes in the experimental design (although the well-known sensitivity to microphysics is still apparent). This talk will highlight the successful analysis of this event and discuss the mechanics of the EnKF procedure applied to a real and complex convective situation. In addition, the relative merits of 1-h forecasts produced from the EnKF analyses and the many outstanding issues that need to be addressed before these techniques can be applied in real time will be discussed.

Available online at ://http://ams.confex.com/ams/pdfpapers/124285.pdf.

Coniglio, M. C., J. S. Kain, S. J. Weiss, M. Xue, M. L. Weisman, Z. I. Janjic, 2007: Evaluating storm-scale model output for severe-weather forecasting: The 2007 NOAA HWT Spring Experiment.. Preprints, 4th European Conference on Severe Storms, Trieste, Italy, International Centre for Theoretical Physics, CD-ROM, 03.11.

Coniglio, M. C., A. E. Cohen, S. F. Corfidi, S. J. Corfidi, 2007: Discrimination of MCS environments using sounding observations. Weather and Forecasting, 22, 1045-1062.

The prediction of the strength of mesoscale convective systems (MCSs) is a major concern to operational meteorologists and the public. To address this forecast problem, this study examines meteorological variables derived from sounding observations taken in the environment of quasi-linear MCSs. A set of 186 soundings that sampled the beginning and mature stages of the MCSs are categorized by their production of severe surface winds into weak, severe, and derecho-producing MCSs. Differences in the variables among these three MCS categories are identified and discussed. Mean low- to upper-level wind speeds and deep-layer vertical wind shear, especially the component perpendicular to the convective line, are excellent discriminators among all three categories. Low-level inflow relative to the system is found to be an excellent discriminator, largely because of the strong relationship of system severity to system speed. Examination of the mean wind and shear vectors relative to MCS motion suggests that cell propagation along the direction of cell advection is a trait that separates severe, long-lived MCSs from the slower-moving, nonsevere variety and that this is favored when both the deep-layer shear vector and the mean deep-layer wind are large and nearly parallel. Midlevel environmental lapse rates are found to be very good discriminators among all three MCS categories, while vertical differences in equivalent potential temperature and CAPE only discriminate well between weak and severe/derecho MCS environments. Knowledge of these variables and their distribution among the different categories of MCS intensity can be used to improve forecasts and convective watches for organized convective wind events.

Coniglio, M. C., J. S. Kain, S. J. Weiss, D. R. Bright, J. J. Levit, M. Xue, M. L. Weisman, Z. I. Janjic, M. Pyle, J. Du, D. J. Stensrud, 2007: Evaluating WRF model output for severe-weather forecasting: The 2007 NOAA HWT Spring Experiment.. Extended Abstracts, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, American Meteorological Society, CD-ROM, 11A.2.

Coniglio, M. C., M. Bardon, K. Virts, S. J. Weiss, 2006: Forecasting the maintenance of mesoscale convective systems.. Extended Abstracts, 23rd Conf. on Severe Local Storms, St. Louis, MO, USA, American Meteorological Society, CD-ROM, 2.3.

Coniglio, M. C., J. S. Kain, S. J. Weiss, D. R. Bright, J. J. Levit, G. W. Carbin, K. W. Thomas, F. Kong, M. Xue, M. L. Weisman, M. E. Pyle, K. L. Elmore, 2008: Evaluation of WRF model output for severe-weather forecasting from the 2008 NOAA Hazardous Weather Testbed Spring Experiment. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor. Soc., CD-ROM, 12.4. [Available from Michael C. Coniglio, NSSL, 120 David L. Boren Blvd., Norman, OK, USA, 73072.]

Available online at ://http://ams.confex.com/ams/24SLS/techprogram/paper_142060.htm.

Diffenbaugh, N. S., R. J. Trapp, H. E. Brooks, 2008: Does Global Warming Influence Tornado Activity?. EOS, TRANSACTIONS, AMERICAN GEOPHYSICAL UNION, 89, 533-534.

Tornadoes and other severe thunderstorm phenomena frequently cause as much annual property damage in the United States as do hurricanes, and often cause more fatalities (see http://www.nws.noaa.gov/om/hazstats.shtml). In 2008, there were 2176 preliminary tornado reports logged through mid-December, with 1600 “actual counts” (duplicate reports removed) through September, the highest total in the past half century (Figure 1). The mass media have covered these events extensively, and experts have been deluged with requests for explanations, including possible links to anthropogenic global warming. Although recent research has yielded insight into the connections between global warming and tornado and severe thunderstorm forcing, these relationships remain mostly unexplored, largely because of the challenges in observing and numerically simulating tornadoes. Indeed, a number of questions that have been answered for other climate-related phenomena remain particularly difficult for climate and severe weather scientists, including whether there are detectable trends in tornado occurrence and if so, what causes them. This article explores the challenges and opportunities in pursuing these areas of research.

Available online at ://http://www.agu.org/journals/eo/eo0853/2008EO530001.pdf.

Doswell III, C. A., H. E. Brooks, M. P. Kay, 2005: Climatological estimates of daily local nontornadic severe thunderstorm probability for the United States. Weather and Forecasting, 20, 577-595.

The probability of nontornadic severe weather event reports near any location in the United States for any day of the year has been estimated. Gaussian smoothers in space and time have been applied to the observed record of severe thunderstorm occurrence from 1980 to 1994 to produce daily maps and annual cycles at any point. Many aspects of this climatology have been identified in previous work, but the method allows for the consideration of the record in several new ways. A review of the raw data, broken down in various ways, reveals that numerous nonmeteorological artifacts are present in the raw data. These are predominantly associated with the marginal nontornadic severe thunderstorm events, including an enormous growth in the number of severe weather reports since the mid-1950s. Much of this growth may be associated with a drive to improve warning verification scores. The smoothed spatial and temporal distributions of the probability of nontornadic severe thunderstorm events are presented in several ways. The distribution of significant nontornadic severe thunderstorm reports (wind speeds 65 kt and/or hailstone diameters 2 in.) is consistent with the hypothesis that supercells are responsible for the majority of such reports.

Doswell III, C. A., H. E. Brooks, N. Dotzek, 2009: On the implementation of the enhanced Fujita scale in the USA. Atmospheric Research, 93, 554-563.

The history of tornado intensity rating in the United States of America (USA), pioneered by T. Fujita, is reviewed, showing that non-meteorological changes in the climatology of the tornado intensity ratings are likely, raising questions about the temporal (and spatial) consistency of the ratings. Although the Fujita scale (F-scale) originally was formulated as a peak wind speed scale for tornadoes, it necessarily has been implemented using damage to estimate the wind speed. Complexities of the damage-wind speed relationship are discussed.

Recently, the Fujita scale has been replaced in the USA as the official system for rating tornado intensity by the so-called Enhanced Fujita scale (EF-scale). Several features of the new rating system are reviewed and discussed in the context of a proposed set of desirable features of a tornado intensity rating system.

It is concluded that adoption of the EF-scale in the USA may have been premature, especially if it is to serve as a model for how to rate tornado intensity outside of the USA. This is in large part because its degree of damage measures used for estimating wind speeds are based on USA-specific construction practices. It is also concluded that the USA's tornado intensity rating system has been compromised by secular changes in how the F-scale has been applied, most recently by the adoption of the EF-scale. Several recommendations are offered as possible ways to help develop an improved rating system that will be applicable worldwide.

Douglas, M., J. M. Galvez, J. F. Mejia, C. Brown, R. Orozco, C. Watts, 2005: Seasonal evolution of the sea-land breeze circulation and its role in the precipitation climatology of northwestern Mexico. Preprints, 6th Conference on Coastal Atmospheric and Oceanic Prediction and Processes (6COASTAL), San Diego, CA, USA, American Meteorological Society, CD-ROM, 3.7.

Douglas, M. W., J. Mejia, J. Murillo, R. Orozco, 2007: Spatial Structure of Cloudiness Associated with the Mid-Summer Drought from MODIS and GOES Imagery. Extended Abstracts, AGU Joint Assembly, Acapulco, Mexico, AGU, H51G-04.

Douglas, M. W., R. Orozco, J. F. Mejia, 2008: Mapping the spatial extent of the Central American mid-summer drought with MODIS and GOES imagery. Preprints, 28th Conference on Hurricanes and Tropical Meteorology, Orlando, FL, USA, American Meteorological Society, P1C.10. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

Many parts of Central America and southern Mexico experience an extended dry period within the longer period of summer rains. This mid-summer drought (MSD), usually during July and August, shows a complicated spatial structure, reflecting the interaction of the large-scale synoptic flow and the varied topography of the region. We have used MODIS imagery (250 m resolution) and GOES 10 km imagery for the years 1983 to 2006 to describe the spatial structure of the cloudiness associated with the MSD. Compositing results using specific periods and also by using different indices (trade wind intensity and cloudiness over specific domains) will be shown. The importance (and challenge) of identifying suitable indices that represent the MSD will be discussed.

Douglas, M. W., J. F. Mejia, 2008: Aircraft measurements of temperature anomalies associated with tropical waves during NAMMA. Preprints, 28th Conference on Hurricanes and Tropical Meteorology, Orlando, FL, USA, American Meteorological Society, P1E.4. [Available from Michael W Douglas, 120, Norman, OK, USA, 73072.]

Special measurements were made of tropical waves over the far eastern tropical Atlantic during the NASA-AMMA field program during August and September 2006. One objective of this program was to help determine why some waves develop rapidly into tropical storms while most do not. This presentation shows the temperature anomalies associated with the different waves sampled by the dropsonde and flight level data from the NASA DC-8 and also other estimates of the temperature field from in-situ soundings. The analyses will be compared both with operational global analyses and with mesoscale analyses produced by assimilating the aircraft observations with the WRF model.

Douglas, M. W., J. F. Mejia, R. Orozco, S. Henry, 2008: Quantifying the extent and degree of cloud-affected tropical environments with MODIS imagery. Two extreme environments: Lomas and cloud forests. Preprints, 28th Conference on Hurricanes and Tropical Meteorology, Orlando, FL, USA, American Meteorological Society, 10.1. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

Quantifying the extent and degree of cloud-affected tropical environments with MODIS imagery. Two extreme environments: Lomas and cloud forests

Michael W. Douglas, NOAA/NSSL, Norman, OK; and J. F. Mejia, R. Orozco, and S. Henry

Using a simple algorithm for extracting cloudiness from the visible MODIS imagery we have developed short-period (~ several years) cloudiness climatologies for different tropical regions at 250m spatial resolution. This presentation focuses on two environments that are difficult to accurately delineate with conventional climate data or even current satellite-based rainfall estimation techniques. One such environment, tropical cloud forest, is characterized by very high precipitation and also high cloudiness. However, cloud forest is mostly distinguished from surrounding lowland rain forest by the very high frequency of cloudiness and its small spatial extent. The second environment of our study is the coastal fog/low cloud zone along arid coastlines (known as “lomas” in Peru). These regions receive almost no rainfall, yet have vegetation supported by the frequent low clouds that intercept the topography along the coast. Such areas are even more difficult to identify from raingauges or satellite rainfall estimates than cloud forests.

We have developed a simple algorithm to use the cloudiness frequencies obtained from the MODIS imagery to classify the “intensity” of both the cloud forests and the lomas. The algorithm uses MODIS imagery from the NASA Terra and Aqua satellites to stratify cloudiness by annual amount, seasonality, and diurnal variability. Areas most favorable for vegetation growth are those with maximum annual frequency of cloudiness and minimum seasonality and diurnal variation, other factors being equal.S

Douglas, M. W., J. F. Mejia, J. F. Galvez, J. Murillo, R. Orozco, 2008: West African pilot balloon network during the NAMMA-2006 and implications for the future of the African pilot balloon sounding network.. Preprints, The 88th Annual Meeting (20-24 January 2008) (New Orleans, LA), New Orleans, LA, USA, American Meteorological Society, 15B.5. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

The West African pilot balloon network during the NAMMA-2006 and implications for the future of the African pilot balloon sounding network

Michael W. Douglas, NOAA/NSSL, Norman, OK; and J. Murillo, J. F. Mejia, J. M. Galvez, and R. Orozco

The pilot balloon network in West Africa has been in place for more than 50 years, and in the past the network was characterized by relatively frequent observations (often 4-times daily) and with high spatial density (more than 20 stations in West Africa). Such a network would be potentially very useful in helping to track the African waves that typically evolve into tropical storms over the Atlantic Ocean. However, the pilot balloon network has decayed in recent decades. The NAMMA (NASA-African Monsoon Multidisciplinary Analysis (AMMA)), involving a field campaign in 2006, afforded an opportunity to attempt to re-invigorate the pilot balloon network. One component of NAMMA involved strengthening the pilot balloon wind sounding network over west Africa to help describe the intensity of African waves exiting the continent. Four countries were the focus of this work and 10 stations were visited over the course of one month just prior to the NAMMA. Many technical problems were encountered and dealt with, but many problems were related to the personnel and the organization of the National Meteorological Services of the region. Some success was achieved in making the observations, but considerably less than was initially expected. This talk summarizes the main problems encountered, our short-term solutions, and our perspectives on how renovating this potentially-valuable network may be possible.

Douglas, M. W., J. M. Murillo, R. K. Orozco, J. F. Mejias, 2008: Underutilized observations for studying tropical climate variations: the historical pilot balloon database.. Preprints, The 88th Annual Meeting (20-24 January 2008) (New Orleans, LA), New Orleans, LA, USA, American Meteorological Organization, 3B.6. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

Underutilized observations for studying tropical climate variations: the historical pilot balloon data base

Michael W. Douglas, NOAA/NSSL, Norman, OK; and R. Orozco, J. F. Mejia, and J. Murillo

The longest-running atmospheric sounding data base is that from pilot balloon observations (“pibals”), whose routine observations date from the early 20th century. Such observations are still made today, though mostly in developing countries in Asia and Africa. Although pibals are subject to limitations (cloudiness and darkness being the two most obvious ones), their low cost has historically allowed for more frequent and more widespread use than radiosondes. Much less well-known, and less appreciated, is that pibals have some advantages over radiosonde winds for studies of climate variability. The procedure for making a pibal has not fundamentally changed in 100 years, unlike wind observations obtained from rawinsonde systems – which have used radiotheodolites, Omega, LORAN and now GPS. Wind profiles obtained from these different systems show somewhat differing characteristics, which can complicate identifying historical trends in wind data.

Making effective use of historical pilot balloon data for climate studies requires availability of the original angle data and some metadata - such as the characteristics of the balloons and inflation procedures. We discuss the difficulty in obtaining both of these; a major effort at digitizing the global data base of pilot balloon observations will be required. Studies are underway (results will be shown) to evaluate the uncertainties introduced into mean wind profiles due to missing data (generally due to clouds), and the observational errors that characterize different pibal networks. These need to be known to determine the limitations of pibals for describing and monitoring regional climate variations.

Douglas, M. W., J. Murillo, J. F. Mejia, 2008: Two courses missing from meteorology programs at US universities.. Preprints, The 88th Annual Meeting (20-24 January 2008) (New Orleans, LA), New Orleans, LA, USA, American Meteorological Society, P1.35. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

Two courses missing from US university meteorology programs

Michael W. Douglas, NOAA/NSSL, Norman, OK; and J. Murillo and J. F. Mejia

This presentation describes the need for, and potential content of, two meteorological courses usually lacking in meteorology programs at US universities. These subjects are somewhat related and potentially could be combined into one course. The first subject is that of “Design and execution of field programs in the atmospheric sciences”. While it might be argued that there is such diversity in meteorological field activities that “hands-on” learning is best, there are many aspects common to most field studies that students could benefit from via formal lectures. Such a course might best be taught at the advanced graduate level, where students are closer to participating in, and perhaps helping design, such activities. The second, somewhat complementary course, might be titled “International Meteorological Activities and the functions of National Meteorological Services”. Rarely are US students (unlike foreign students) exposed to the enormous variety of meteorological activities that occur globally. An equally small number of students have a good conceptual understanding of the different components of any National Meteorological Service (including that of the US). Material common to both courses would include covering the existing (and research) observing systems across the globe – this material is often left out of courses on meteorological instrumentation.

Motivation for developing this material has come from the development of courses for international audiences with widely varying backgrounds. A sample syllabus will be provided to stimulate discussion.

Douglas, M. W., J. Murillo, R. Orozco, J. M. Galvez, J. F. Mejia, 2006: Accuracy of the Aviation Model (AVN) final analyses over Central South America based upon upper air observations collected during the SALLJEX.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, AMS, PC1-24.

Douglas, M. W., J. M. Galvez, C. R. Reyes, R. Orozco, 2006: Observed diurnal circulations and rainfall over the altiplano during the SALLJEX.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, American Meteorological Society, PA1-9.

Douglas, M. W., J. M. Galvez, 2006: Modulation of rainfall by Lake Titicaca using the WRF Model.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, American Meteorological Society, PB1-21.

Douglas, M. W., J. M. Galvez, 2006: Northward-propagating surges east of the Andes during the SALLJEX.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, American Meteorological Society, PB3-33.

Douglas, M. W., J. F. Mejia, 2006: Flow around the Andean elbow from WRF simulations and P-3 aircraft measurements during SALLJEX.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, American Meteorological Society, PB3-32.

Douglas, M. W., J. M. Galvez, R. Orozco, J. F. Mejjia, 2006: Plausible effects of Paleolake Tauca on the altiplano circulations and rainfall from WRF model simulations.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, American Meteorological Society, PB3-34.

Douglas, M. W., J. Regalado, J. Murillo, 2006: Atmospheric soundings across an oceanic front between the Galapagos Islands and the coast of South America from the INOCAR cruise of October 2005.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, American Meteorological Society, PA3-33. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

Special radiosonde observations were made from the INOCAR research vessel Orion during the
second INOCAR oceanographic cruise of 2005. These observations were carried out for both
operational and scientific objectives. Operationally, we sought to evaluate the feasibility of
routinely making radiosonde observations from the ship, and determining what the ship might
need for such observations. Since relatively few upper air observations have been made
between the Galapagos Islands and the coast of Ecuador we wanted to obtain high spatial
resolution soundings across the equatorial cold tongue, which has been the subject of recent
research measurements farther west in the eastern Pacific. Some results of the boundary layer
over the cold tongue, based on the radiosonde measurements, are reported here. With some
modifications, the Orion is a suitable platform for routine atmospheric measurements in this
poorly sampled region of the eastern Pacific.

Douglas, M. W., L. Florez, N. Ordinola, J. Murillo, 2006: Variability of the meridional flow near the Equator from 8 years of pilot balloon observations at Piura, Peru.. Preprints, 8th International Conference on Southern Hemisphere Meteorology and Oceanography (ICSHMO), Foz do Iguazu, Brazil, American Meteorological Society, PD3-14. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, Brazil, 73072.]

Pilot balloon observations have been made at Piura, Peru since 1997 as part of the PACS–SONET project. This data set is the most complete set of observations from SONET, andillustrates the value of a single station’s multi-year record for studies of interannual variability ofthe windfield near the equator.

Douglas, M. W., R. Orozco, J. M. Galvez, J. Murillo, J. F. Mejia, 2006: The seasonal evolution of the diurnal variation of the low-level winds around the Gulf of California. Is there a link to vegetation green-up during the wet season?. Preprints, 86th American Meteorological Annual Meeting (18th Conference on Climate Variability and Change), Atlanta, GA, Atlanta, GA, USA, American Meteorological Society, J3.4. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

Sea-land breeze circulations are ubiquitous along the Gulf of California. Sea breezes are well developed because of the strong heating over the desertic regions along both sides of the Gulf. However, the sea surface temperature has a large seasonal range, especially over the northern Gulf. In addition, after the start of the summer rains there is a rapid foliation of the seasonal dry forest found along the eastern side of the Gulf. It was hypothesized that the rapid vegetation change and associated change in the land surface characteristics (albedo and evapotranspiration) might modify the sea-land breeze circulations. This might in turn affect the diurnal evolution of rainfall over the region. The recently ended North American Monsoon Experiment (NAME) afforded an opportunity to determine the possible seasonal variation of the sea-breeze intensity and its relationship with the onset of the rainy season. This presentation will describe the effort to measure the diurnal cycle of the winds and its seasonal variation. A network of 7 pilot balloon stations made observations twice-daily for approximately four months, with two of these making more frequent observations during special periods. Surface observations from automated surface stations were also available. The monthly mean winds from the different stations will be shown, as well as divergence estimates over different subregions of the pilot balloon array. The changes in sea-breeze intensity and the area-averaged divergence estimates will be compared with the seasonal evolution of the Gulf surface temperature and mean land surface temperature changes and the observed rainfall onset over the region.

Douglas, M. W., R. Orozco, J. M. Galvez, 2006: Diurnal variability of the cloud field over the VOCALS domain from GOES imagery.. Preprints, 86th American Meteorological Annual Meeting (14th Conference on Interaction of the Sea and Atmosphere), Atlanta, GA, USA, American Meteorological Society, P1.3. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

As part of ongoing studies of mesoscale variability over the South American altiplano we have produced averages of the cloudiness using GOES imagery. These composites are made at full resolution of the imagery, to help identify the relationship between the underlying topography and the cloud field. The upcoming VOCALS activity, focused on the stratocumulus region of the southeastern Pacific, has as one objective the description of the diurnal cycle of this cloudiness and its relationship to the South American continent. With this in mind, we have produced GOES imagery composites for the SE Pacific with 30 min temporal resolution. These composites show the diurnal variation of the cloudiness and its apparent propagation offshore. The composites are stratified by time of year. Comparison is made with the simulated diurnal cycles reported in the literature.

Douglas, M. W., T. Killeen, J. F. Mejia, 2006: Use of MODIS and GOES imagery to help delineate the distribution of cloud forests along the eastern Andean slopes.. Preprints, (14th Conference on Satellite Meteorology and Oceanography), Atlanta, GA, USA, American Meteorological Society, P3.18. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

The environment with the greatest biodiversity from a global standpoint is that known as the tropical Andes “hotspot”, which is a broad region along the eastern slopes of the Andes in South America. One of the subregions with the highest diversity within this region is the cloud forest, a region of very high cloudiness and high annual precipitation. Mapping the cloud forest and surrounding environments has been of high priority because resources for conservation are limited and conservation organizations and governmental agencies need to know what areas should receive highest priority for protection efforts.

Work associated with the South American Low-level Jet Experiment (SALLJEX) carried out in 2002-3 led to the use of GOES imagery to develop composites of visible and IR imagery for describing the mean cloudiness along the eastern slopes of the Andes. More recently MODIS imagery has been used to describe cloudiness at even higher resolution. Together, these imagery sources provide clues as to the distribution of cloudiness that can be related to cloud forest environment. In addition, dry canyon environments, the locus of many geographically-restricted species, can likewise be readily described from the cloudiness composites.

The GOES and MODIS cloudiness composites will be shown, and some limitations of inferring cloud forest locations and dry canyon habitat from the imagery will be discussed. The potential for this technique to be applied to other areas will be mentioned.

Douglas, M. W., N. Ordinola, J. F. Mejia, 2005: Rainfall variations along the coast of Peru and Ecuador during the 1997–8 El Niño and implications for a real-time forecasting system over the region. Preprints, Ninth Symposium on Integrated Observing and Assimilation Systems for the Atmosphere, Oceans, and Land Surface (IOAS-AOLS), 85th AMS Annual Meeting, San Diego, CA, USA, American Meterological Society, 5.2. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

Special observations collected during the 1997-8 El Niño event along the coast of Peru and Ecuador have been re-evaluated, together with NCEP reanalyses and satellite imagery for the period. We had previously composited the special pilot balloon observations with respect to rainfall measurements made over the region to describe the wet- and dry-day characteristics. Recently, we have generated composites of satellite imagery and meteorological fields derived from the NCEP reanalyses and we have revised the composites done previously. We will show the mean fields associated with wet and dry days, together with the evolution of these fields. Satellite composites for the different periods will also be shown. Using these results we discuss the implications for a weather forecasting network over the region that experiences little rainfall, but when it occurs it is very important. The kinds of observations that might be needed for such a network, which might be temporary rather than permanent, are outlined. .

Douglas, M. W., J. Murillo, 2005: Reasons for the failure of the Pan American Climate Studies Sounding Network (PACS-SONET) in Latin America.. Preprints, Ninth Symposium on Integrated Observing and Assimilation Systems for the Atmosphere, Oceans, and Land Surface (IOAS-AOLS), San Diego, CA, USA, American Meteorological Society, p1.18. [Available from Michael W Douglas, 120 David Boren Boulevard, Norman, OK, USA, 73072.]

NOAA's Office of Global Programs has supported a network of pilot balloon stations in Latin America to provide wind measurements in areas where few observations previously existed. This network has existed since 1997 in various forms, with up to 20 sites providing daily or twice-daily observations. Although some success has been obtained, the network has not succeeded in obtaining self-sustainability within the host countries. This presentation will discuss some of the factors that have prevented a sustainable climate monitoring upper air network from being achieved. Many logistical factors have complicated the network's operation, but we feel that the main problem lies within the educational arena of the countries involved. The lack of meteorologically-educated personnel throughout the weather services and other institutions of the region has prevented and thorough understanding of the objectives of the network. In addition, the emphasis on inexpensive technology may have also generated the perception that the activity was not important because of the low overall cost. Some of these perception problems will be discussed in this presentation . A strategy for maintaining a self-sustaining activity will be outlined, though its feasibility may be in doubt.

Douglas, M. W., J. Murillo, J. F. Mejia, 2005: Conducting short duration field programs to evaluate sounding site representativness and potential climate monitoring biases-Examining the Low-Level Jet Over the Venezuelan Llanos During the 2005 Dry Season. Preprints, 13th Symposium on Meteorological Observations and Instrumentation, Savannah, GA, USA, American Meteorological Society, JP1.32.

Douglas, M. W., R. Orozco, J. M. Galvez, 2005: Measuring and monitoring the mesoclimate of tropical locations. Field observations from the South American altiplano during the SALLJEX. Preprints, 13th Symposium on Meteorological Observations and Instrumentation, Savannah, GA, USA, American Meteorological Society, 6.2.

Douglas, M. W., 2008: The Pan American Climate Studies Sounding Network. Bulletin of the American Meteorological Society, 89, 1709-1725.

A research effort primarily involving pilot balloon observations was carried out during the summer of 1997 to study rainfall variability over Central America. This activity, supported by NOAA's Pan American Climate Studies (PACS) program, grew in scope in response to the strong El Niño event of 1997/98 and subsequently evolved into a network ranging from Mexico to Paraguay. The overall goal of the PACS-Sounding Network (PACS-SONET) was to obtain relatively inexpensive wind profiles for describing climate variability over parts of the intertropical Americas that were not well covered by routine radiosonde observations. Major portions of the project supported climate research programs focusing on both the South and North American monsoon systems, while other parts of the network provided multiyear observations across important gaps in the Central American cordillera and also helped to describe cross-equatorial flow variations in the eastern Pacific. Approximately 50,000 observations were made by the PACS-SONET over its 10-yr operation.

This paper describes the motivation for and evolution of the network, the logistical complications that were involved in establishing and operating a long-term multinational network, and some of the important results from analysis of the data. We conclude by discussing some of our perspectives on why the network was unable to make a transition from research funding to one supported by meteorological services of the region.

Douglas, M. W., J. Mejia, R. Orozco, J. Murillo, 2008: Suggestions for upgrading the pilot balloon network in West Africa and elsewhere in the tropics. Extended Abstracts, TECO-2008 - WMO Technical Conference on Meteorological and Environmental Instruments and Methods of Observation, St. Petersburg, Russian Federation, World Meteorological Organization, 1(9).

Based on experience during the 2006 NAMMA field program we provide some recommendations for improving the pilot balloon network over the West Africa region. These range from relatively straightforward suggestions as to adjusting the launch time to maximize sounding height, to improved efforts to maintain the equipment and train observers. The supply of gas for balloon inflation is probably the largest logistical problem, followed by quality control of the data. The paper concludes by suggesting that the fastest way to upgrade the sounding network over Africa is to make it independent of National Meteorological Services and place it under an independent body that would oversee all aspects of its operation – for the benefit of Numerical Weather Prediction and climate monitoring objectives. The reasons for this seemingly drastic action are presented.

Available online at ://http://www.knmi.nl/samenw/geoss/wmo/TECO2008/IOM-96-TECO2008/1(09)_Douglas_USA.pdf.

Douglas, M. W., 2008: Progress towards development of the glidersonde: a recoverable radiosonde system. Extended Abstracts, TECO-2008 - WMO Technical Conference on Meteorological and Environmental Instruments and Methods of Observation, St. Petersburg, Russian Federation, World Meteorological Organization, P1(6).

The motivation and history of development of a recoverable radiosonde system using a glider lifted aloft by a radiosonde balloon – the “glidersonde”, is summarized in this poster. The current status of development efforts currently involve at least three separate groups; in the USA, in South Africa, and a version, developed in New Zealand, is now being marketed commercially. These efforts are briefly summarized, as are some limitations that still need to be overcome for widespread adoption of such technology.

Available online at ://http://www.knmi.nl/samenw/geoss/wmo/TECO2008/IOM-96-TECO2008/P1(06)_Douglas_USA.pdf.

Douglas, M. W., J. Mejia, N. Ordinola, J. Boustead, 2009: Synoptic Variability of Rainfall and Cloudiness along the Coasts of Northern Peru and Ecuador during the 1997/98 El Niño Event. Monthly Weather Review, 137, 116-136.

This paper describes the meteorological conditions associated with large fluctuations in rainfall over the coastal regions of northern Peru and Ecuador during the 1997/98 El Niño event. Using data from a network of routine rain gauges and special gauges established just prior to the onset of heavy rains, it is shown that large variations in the daily rainfall on quasi-weekly time scales occurred during the period January–April 1998. These rainfall fluctuations were approximately in phase along the coast from near the equator to ∼7°S. The daily rainfall data was averaged to develop a subset of wet and dry days, and then these dates were used as the basis for compositing. Special pilot balloon observations were composited with respect to the wet and dry days, showing that westerly and northerly wind anomalies are associated with wet spells. Composites of the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis and outgoing longwave radiation (OLR) data support a modest association of anomalous westerly wind events with enhanced rainfall.

The relationship observed between westerly zonal wind anomalies and rainfall west of the Andes during 1998 suggested using the NCEP reanalysis to develop composites based on westerly wind events observed during other years. Zonal wind anomalies at 700 hPa were used as the primary criterion for stratifying “wet” and “dry” days, despite reservations about the association between rainfall and zonal wind. Compositing Geostationary Operational Environmental Satellite (GOES) and OLR data for 220 west wind anomaly events from the months of January–April for the years 1990–2005 showed that they are associated with enhanced cloudiness that propagates eastward at ∼10 m s−1. The composites using NCEP reanalyses show the evolution of the wind field associated with the wet days and suggest a link between extratropical wave passages across North America and anomalous westerly wind events off the coast of Ecuador and northern Peru.

Engerer, N. A., D. J. Stensrud, M. C. Coniglio, 2008: Surface Characteristics of Observed Cold Pools. Monthly Weather Review, 136, 4839-4849.

Cold pools are a key element in the organization of precipitating convective systems, yet knowledge of their typical surface characteristics is largely anecdotal. To help alleviate this situation, cold pools from 39 mesoscale convective system (MCS) events are sampled using Oklahoma Mesonet surface observations. One thousand three hundred and eighty-nine time series of surface observations are used to determine typical rises in surface pressure and decreases in temperature, potential temperature, and equivalent potential temperature associated with the cold pool, and the maximum wind speeds in the cold pool. The data are separated into one of four convective system lifecycle stages: first storms, MCS initiation, mature MCS, and MCS dissipation. Results indicate that the mean surface pressure rises associated with cold pools increase from 3.2 hPa for the first storms lifecycle stage to 4.5 hPa for the mature MCS stage before dropping to 3.3 hPa for the dissipation stage. In contrast, the mean temperature (potential temperature) deficits associated with cold pools decrease from 9.5 K (9.8 K) to 5.4 K (5.6 K) from the first storms to dissipation stage, with a decrease of approximately 1 K associated with each advance in lifecycle stage. However, the daytime and early evening observations show mean temperature deficits over 11 K. A comparison of these observed cold pool characteristics with results from idealized numerical simulations of MCSs suggests that observed cold pools likely are stronger than those found in model simulations, particularly when ice processes are neglected in the microphysics parameterization. The mean deficits in equivalent potential temperature also decrease with MCS lifecycle stage, starting at 21.6 K for first storms and dropping to 13.9 K for dissipation. Mean wind gusts are above 15 m s-1 for all lifecycle stages. These results should help numerical modelers determine if the cold pools in high-resolution models are in reasonable agreement with the observed characteristics found herein. Thunderstorm simulations and forecasts with thin model layers near the surface also are needed to obtain better representations of cold pool surface characteristics that can be compared with observations.

Gilleland, E., M. Pocernich, H. E. Brooks, 2006: Analyzing the Extreme Behavior of Large-Scale Meteorlogical Variables Found To Have Influence on Severe Storms and Tornadic Events Using Global Reanalysis Data. Extended Abstracts, 2006 Joint Statistical Meetings (JSM) of the American Statistical Association (ASA): Statistics for an uncertain world: Meeting global challenges, Seattle, WA, USA, American Statistical Association, 453-453.

Gutowski, Jr., W. J., G. C. Hegerl, G. J. Holland, T. R. Knutson, L. O. Mearns, R. J. Stouffer, P. J. Webster, M. F. Wehner, F. W. Zwiers, H. E. Brooks, K. A. Emanuel, P. D. Komar, J. P. Kossin, K. E. Kunkel, R. McDonald, G. A. Meehl, R. J. Trapp, 2008: Causes of Observed Changes in Extremes and Projections of Future Changes. Weather and Climate Extremes in a Changing Climate Regions of Focus: North America, Hawaii, Caribbean, and U.S. Pacific Islands: Synthesis and Assessment Product 3.3 Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change, T. R. Karl, G. A. Meehl, C. D. Miller, S. J. Hassol, A. M. Waple, W. L. Murray, Ed(s)., U.S. Climate Change Science Program and the Subcommittee on Glob, 81-116.

Hamill, T. M., R. Schneider, H. E. Brooks, G. Forbes, H. B. Bluestein, M. Steinberg, D. Melendez, R. M. Dole, 2005: The May 2003 extended tornado outbreak. Bulletin of the American Meteorological Society, 86, 531-542.

In May 2003 there was a very destructive extended outbreak of tornadoes across the central and eastern United States. More than a dozen tornadoes struck each day from 3 May to 11 May 2003. This outbreak caused 41 fatalities, 642 injuries, and approximately $829 million dollars of property damage. The outbreak set a record for most tornadoes ever reported in a week (334 between 4-10 May), and strong tornadoes (F2 or greater) occurred in an unbroken sequence of nine straight days. Fortunately, despite this being one of the largest extended outbreaks of tornadoes on record, it did not cause as many fatalities as in the few comparable past outbreaks, due in large measure to the warning efforts of National Weather Service, television, and private-company forecasters and the smaller number of violent (F4-F5) tornadoes. This event was also relatively predictable; the onset of the outbreak was forecast skillfully many days in advance.

An unusually persistent upper-level trough in the intermountain west and sustained low-level southerly winds through the southern Great Plains produced the extended period of tornado-favorable conditions. Three other extended outbreaks in the past 88 years were statistically comparable to this outbreak, and two short-duration events (Palm Sunday 1965 and the 1974 Superoutbreak) were comparable in the overall number of strong tornadoes. An analysis of tornado statistics and environmental conditions indicates that extended outbreaks of this character occur roughly every 10 to 100 years.

Heinselman, P., S. Weiss, M. Coniglio, D. Andra, G. Stumpf, B. Phillips, J. Brotzge, cited 2008: 2008 Spring HWT Experiments at the NWC. [Available online at ://http://www.nwas.org/newsletters/pdf/news_october2008.pdf.]

Higgins, W., D. Ahijevych, J. Amador, A. Barros, E. Berbery, E. Caetano, R. Carbone, P. Ciesielski, R. Cifelli, M. Cortez-Vazquez, A. Douglas, M. Douglas, G. Emmanuel, C. Fairall, D. Gochis, D. Gutzler, T. Jackson, R. Johnson, C. King, T. Lang, M. Lee, D. Lettenmaier, R. Lobato, V. Magaña, J. Meitin, K. Mo, S. Nesbitt, F. Ocampo-Torres, E. Pytlak, P. Rodgers, S. Rutledge, J. Schemm, S. Schubert, A. White, C. Williams, A. Wood, R. Zamora, C. Zhang, 2006: The NAME 2004 Field Campaign and Modeling Strategy. Bulletin of the American Meteorological Society, 87, 79-94.

Kain, J. S., S. J. Weiss, J. J. Levit, M. E. Baldwin, D. R. Bright, 2006: Examination of convection-allowing configurations of the WRF model for the prediction of severe convective weather: The SPC/NSSL Spring Program 2004. Weather and Forecasting, 21, 167-181.

Convection-allowing configurations of the Weather Research and Forecast (WRF) model were evaluated during the 2004 Storm Prediction Center–National Severe Storms Laboratory Spring Program in a simulated severe weather forecasting environment. The utility of the WRF forecasts was assessed in two different ways. First, WRF output was used in the preparation of daily experimental human forecasts for severe weather. These forecasts were compared with corresponding predictions made without access to WRF data to provide a measure of the impact of the experimental data on the human decision-making process. Second, WRF output was compared directly with output from current operational forecast models. Results indicate that human forecasts showed a small, but measurable, improvement when forecasters had access to the high-resolution WRF output and, in the mean, the WRF output received higher ratings than the operational Eta Model on subjective performance measures related to convective initiation, evolution, and mode. The results suggest that convection-allowing models have the potential to provide a value-added benefit to the traditional guidance package used by severe weather forecasters.

Kain, J. S., S. J. Weiss, D. R. Bright, M. E. Baldwin, J. J. Levit, G. W. Carbin, C. S. Schwartz, M. L. Weisman, K. K. Droegemeier, D. B. Weber, K. W. Thomas, 2007: Some practical considerations for the first generation of operational convection-allowing NWP: How much resolution is enough?. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 3B.5.

Kain, J. S., S. J. Weiss, D. R. Bright, M. E. Baldwin, J. J. Levit, G. W. Carbin, C. S. Schwartz, M. L. Weisman, K. K. Droegemeier, D. B. Weber, K. W. Thomas, 2008: Some practical considerations regarding horizontal resolution in the first generation of operational convection-allowing NWP. Weather and Forecasting, 23, 931-952.

During the 2005 NOAA Hazardous Weather Testbed Spring Experiment two different highresolution
configurations of the WRF-ARW model were used to produce 30 h forecasts five days
a week for a total of 7 weeks. These configurations used the same physical parameterizations and
the same input dataset for initial and boundary conditions, differing primarily in their spatial resolution.
The first set of runs used 4 km horizontal grid spacing with 35 vertical levels while the
second used 2 km grid spacing and 51 vertical levels.
Output from these daily forecasts is analyzed to assess the numerical forecast sensitivity to
spatial resolution in the upper end of the convection-allowing range of grid-spacing. The analysis
is based on a combination of visual comparison, systematic subjective verification conducted during
the Spring Experiment, and objective metrics based largely on the mean diurnal cycle of simulated
reflectivity and precipitation fields. Additional insight is gained by examining the size
distributions of individual reflectivity and precipitation entities and by comparing forecasts of
mesoscyclone characteristics in the two sets of forecasts.
In general, the 2 km forecasts provide more detailed presentations of convective activity, but
there appears to be little, if any, forecast skill on the scales where the added details emerge. On
the scales where both model configurations show higher levels of skill - the scale of mesoscale
convective features - the forecasts appear to provide comparable utility for severe weather forecasters.
These results suggest that 4 km grid spacing is a good place to start for the first generation
of 1-2 day convection-permitting operational NWP.

Kain, J. S., S. J. Weiss, D. R. Bright, M. E. Baldwin, J. J. Levit, G. W. Carbin, C. S. Schwartz, M. L. Weisman, K. K. Droegemeier, 2007: Some practical considerations for the first generation of operational convection-allowing NWP: How much resolution is enough?. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 3B.5. [Available from John S. Kain, NSSL, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

During the 2005 NOAA Hazardous Weather Testbed Spring Experiment (formerly known as the SPC/NSSL Spring Program) two different high-resolution configurations of the WRF-ARW model were used to produce 30 h forecasts five days a week for a total of 7 weeks. These configurations used the same physical parameterizations and the same input dataset for initial and boundary conditions, differing primarily in their spatial resolution. The first set of runs used 4 km horizontal grid spacing with 35 vertical levels while the second used 2 km grid spacing and 51 vertical levels.

This setup provided an unprecedented opportunity to assess the sensitivity to spatial resolution in the upper end of the convection-allowing range of grid-spacing, during many different severe-weather events. Of particular interest was whether the ~ ten fold increase in computing expense required by the 2 km runs could be justified by added value in the higher resolution forecasts. In this study, we examine and compare these forecasts from several different perspectives. First, we provide a visual examination of simulated reflectivity fields from selected convective events, highlighting the differences that might be detected by an operational forecaster – differences between the two model runs and the ways that both differ from observed reflectivity fields. Next, we present the results of subjective assessments of forecast skill, based on daily ratings assigned by panels of experts during the Spring Experiment. Then, we move on to objective measures of skill. These measures are based on time-averaged behavior characteristics of the models rather than selected points in time and space. For example, we examine the mean diurnal trends of simulated reflectivity and accumulated precipitation fields, as compared with observations. We compare the size distributions of individual reflectivity and precipitation entities, or “storms”, and we look at measures of storm rotation. Further, we look at traditional verification statistics such as equitable-threat and bias scores.

In general, we find that meteorological fields from the two model configurations behave much more like each other than like observations. The 2 km forecasts provide more detailed structures and appear to provide more realistic depictions of supercell-like storm configurations, both of which are intriguing to severe weather forecasters, but neither configuration shows much skill in predicting these small-scale features. On the scales where they show higher levels of skill – the scale of mesoscale convective features – the forecasts are often quite similar. The implications of these results, i.e., the value added by doubling resolution in this context, will be discussed at the conference.

Available online at ://http://ams.confex.com/ams/pdfpapers/124513.pdf.

Kain, J. S., S. J. Weiss, S. R. Dembek, J. J. Levit, D. R. Bright, J. L. Case, M. C. Coniglio, A. R. Dean, R. Sobash, 2008: Severe-weather forecast guidance from the first generation of large domain convection-allowing models: Challenges and opportunities. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor Soc., CD-ROM, 12.1. [Available from John Kain, NSSL, 120 David L. Boren Blvd., Norman, OK, USA, 73072.]

Kain, J. S., S. J. Weiss, M. E. Baldwin, 2006: The value of collaboration between researchers and forecasters in the development of NWP models. Preprints, The 4th Joint Korea-U. S. Workshop on Mesoscale Observation, Data Assimilation, and Modeling for Severe Weather, Seoul, Republic of Korea, Korea Science and Engineering Foundation/U.S. National Science F, 6.5. [Available from John Kain, NSSL, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Kain, J. S., S. J. Weiss, M. E. Baldwin, 2006: The value of collaboration between researchers and forecasters in the development of NWP models. Preprints, The 4th Joint Korea-U. S. Workshop on Mesoscale Observation, Data Assimilation, and Modeling for Severe Weather, Seoul, Republic of Korea, Korea Science and Engineering Foundation/U.S. National Science F, 6.5. [Available from John Kain, NSSL, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Killeen, T. J., M. W. Douglas, T. Consiglio, P. M. Jorgensen, J. F. Mejia, 2007: Dry Spots and Wet Spots in the Andean hotspot. Journal of Biogeography, 34, 1357-1373.

Aim To explain the relationship between topography, prevailing winds and precipitation in order to identify regions with contrasting precipitation regimes and then compare floristic similarity among regions in the context of climate change.

Location Eastern slope of the tropical Andes, South America.

Methods We used information sources in the public domain to identify the relationship between geology, topography, prevailing wind patterns and precipitation. Areas with contrasting precipitation regimes were identified and compared for their floristic similarity.

Results We identify spatially separate super-humid, humid and relatively dry regions on the eastern slope of the Andes and show how they are formed by the interaction of prevailing winds, diurnally varying atmospheric circulations and the local topography of the Andes. One key aspect related to the formation of these climatically distinct regions is the South American low-level jet (SALLJ), a relatively steady wind gyre that flows pole-ward along the eastern slopes of the Andes and is part of the gyre associated with the Atlantic trade winds that cross the Amazon Basin. The strongest winds of the SALLJ occur near the 'elbow of the Andes' at 18° S. Super-humid regions with mean annual precipitation greater than 3500 mm, are associated with a 'favourable' combination of topography, wind-flow orientation and local air circulation that favours ascent at certain hours of the day. Much drier regions, with mean annual precipitation less than 1500 mm, are associated with 'unfavourable' topographic orientation with respect to the mean winds and areas of reduced cloudiness produced by local breezes that moderate the cloudiness. We show the distribution of satellite-estimated frequency of cloudiness and offer hypotheses to explain the occurrence of these patterns and to explain regions of anomalously low precipitation in Bolivia and northern Peru. Floristic analysis shows that overall similarity among all circumscribed regions of this study is low; however, similarity among super-humid and humid regions is greater when compared with similarity among dry regions. Spatially separate areas with humid and super-humid precipitation regimes show similarity gradients that are correlated with latitude (proximity) and precipitation.

Main conclusions The distribution of precipitation on the eastern slope of the Andes is not simply correlated with latitude, as is often assumed, but is the result of the interplay between wind and topography. Understanding the phenomena responsible for producing the observed precipitation patterns is important for mapping and modelling biodiversity, as well as for interpreting both past and future climate scenarios and the impact of climate change on biodiversity. Super-humid and dry regions have topographic characteristics that contribute to local climatic stability and may represent ancestral refugia for biodiversity; these regions are a conservation priority due to their unique climatic characteristics and the biodiversity associated with those characteristics.

Koch, S. E., B. S. Ferrier, M. T. Stoelinga, E. Szoke, S. J. Weiss, J. S. Kain, 2005: The use of simulated radar reflectivity fields in the diagnosis of mesoscale phenomena from high-resolution WRF model forecasts. Preprints, 11th Conference on Mesoscale Processes, Albuquerque, NM, USA, Amer. Meteor. Soc., CD-ROM, J4J.7. [Available from Steve Koch, ESRL, Boulder, CO, USA.]

The use of composite radar reflectivity fields (i.e., the maximum reflectivity in the grid column) as a model output product has become increasingly popular recently as a means for display of high-resolution numerical model fields, mainly for convective weather scenarios. This past winter, simulated radar reflectivity fields were produced for 5-km WRF model forecasts during the DTC (Developmental Testbed Center) Winter Forecast Experiment (DWFE). In addition, model reflectivity fields from 2-km and 4-km WRF forecasts were utilized during the annual Storm Prediction Center/National Severe Storms Laboratory (NSSL) Spring Program. The reflectivity product offers significant advantages over traditional precipitation forecast displays, including the obvious fact that radar reflectivity is easier to verify in real time by directly comparing with readily available, observed composite reflectivity products. It has also recently become possible to compare model forecast radar reflectivity fields to a high quality, three-dimensional, national radar reflectivity mosaic product on a 1-km Cartesian grid being developed at NSSL. The chief advantage of the model reflectivity product appears to be that it allows one to more easily see detailed mesoscale and near-stormscale structures capable of being forecast by finer resolution models, such as lake-effect snowbands, the structure of deep convection, and frontal precipitation bands. Examples demonstrating this advantage will be presented at the conference for a variety of mesoscale phenomena.

Before one can have confidence in the meaning of simulated reflectivity factor fields for interpretation of mesoscale models, it is important to understand how they are determined. The equivalent reflectivity factor is computed from the forecast mixing ratios of grid-resolved hydrometeor species, assuming Rayleigh scattering by spherical particles of known density and an exponential size distribution. During the DWFE, perceptible differences appeared in the general nature of the simulated reflectivity fields from the two WRF models, most notably a greater coverage of reflectivity below ~25 dBZ and higher maximum reflectivities in the case of the NMM compared to the ARW for winter storms. However, when attention focused on severe convective weather regions during the Spring Program, the NMM produced noticeably lower values of maximum reflectivity compared to the ARW versions, with the NMM values limited to less than 50 dBZ. These differences are mostly explained by the differences in physics packages, particularly the way various liquid water and ice species are treated in the model microphysics schemes. The WRF Single-Moment 5-class (“WSM5”) microphysics scheme used for the WRF-ARW model during DWFE treats the cloud condensate in the form of cloud water and cloud ice as a combined category, and precipitation in the form of rain and snow also as a combined category. The WRF-NMM used the Ferrier microphysics scheme, which accounts for four classes of hydrometeors. The most important difference between the two microphysical parameterizations concerns the assumed size distributions for snow: for the same snow mass content, differences in radar reflectivity will scale with differences in parameterized snow number concentrations between the two microphysical schemes.

It is also important to understand that it is not possible to make a strictly valid comparison between composite reflectivity computed from a model grid point and that measured by scanning radar. Owing to the fact that the radar resolution degrades with distance from the transmitter, that scanning radars cannot detect hydrometeors in the lower atmosphere due to the earth's curvature effect, and numerous other considerations (including ground clutter near the radar, anomalous propagation, etc.), any attempt to make direct comparisons between the model simulated reflectivity fields and radar measurements is replete with problems, though the NSSL product is experimenting with novel ways to overcome these problems.

Available online at ://http://ams.confex.com/ams/pdfpapers/97032.pdf.

Kong, F., M. XUE, D. R. Bright, M. C. Coniglio, K. W. Thomas, Y. Wang, D. Weber, J. S. Kain, S. J. Weiss, J. Du, 2007: Preliminary analysis on the real-time storm-scale ensemble forecasts produced as a part of the NOAA Hazardous Weather Testbed 2007 Spring Experiment.. Preprints, Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc, CD-ROM, 3B.2.

Kong, F., M. Xue, D. R. Bright, M. C. Coniglio, K. W. Thomas, Y. Wang, D. B. Weber, J. S. Kain, S. J. Weiss, J. Du, 2007: Preliminary analysis on the real-time storm-scale ensemble forecasts produced as a part of the NOAA Hazardous Weather Testbed 2007 Spring Experiment. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 3B.2. [Available from Fanyou Kong, CAPS, 120 David L. Boren Blvd., Norman, OK, USA, 73072.]

A real-time storm-scale WRF-ARW-based ensemble forecast system at 4-km resolution is being developed at CAPS and will be run daily for 33 hours as part of the NOAA Hazardous Weather Testbed (HWT) 2007 Spring Experiment, for a domain covering the eastern 2/3 of the continental U.S. This pilot system consists of ten hybrid perturbation members that consist of a combination of perturbed initial conditions and various microphysics and PBL physics parameterization schemes. The design considerations and the scientific questions that the system intends to address will be presented and discussed.

In addition to traditional ensemble products widely used in large-scale and mesoscale ensemble forecasting systems, such as the mean, spread, and probability of selected forecast fields, emphases are given to the generation and assessment of products specific to storm-scale, cloud-resolving ensemble forecasts. Such products include but are not limited to: probability of storm type (e.g., linear vs. cellular), large hail probability, icing potential (high super-cooled water content probability), damaging wind gusts at surface, reflectivity exceedance, updraft rotation, and supercell thunderstorm detection in the form of probability or joint probability for Supercell Composite Parameter, Significant Tornado Parameter, Supercell Detection Index, and Updraft Helicity. Many of these products are created in real time through existing capabilities in the SPC version of the N-AWIPS system for the use and evaluation by researchers and operational forecasters during the experiment. The statistical consistency of the ensemble system, in terms of spread-error relation, is assessed using the two-months of data after the experiment. The performance of the ensemble forecasts, in terms of quantitative skill scores, is compared with the NCEP operational SREF and 12 km NAM forecasts, and a CAPS 2-km WRF forecast over the same domain and period. Skill scores for sub-groups of the ensemble will be examined to assess the effectiveness of initial condition and physics perturbations.

Available online at ://http://ams.confex.com/ams/pdfpapers/124667.pdf.

Kong, F., M. Xue, K. W. Thomas, Y. Wang, J. S. Kain, S. J. Weiss, D. R. Bright, J. Du, K. K. Droegemeier, 2008: Real-Time Storm-Scale Ensemble Forecast 2008 Spring Experiment. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor. Soc., CD-ROM, 12.3. [Available from Fanyou Kong, CAPS, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Available online at ://http://ams.confex.com/ams/24SLS/techprogram/paper_141827.htm.

Kong, F., M. Xue, K. W. Thomas, Y. Wang, K. A. Brewster, J. Gao, K. K. Droegemeier, J. S. Kain, S. J. Weiss, D. R. Bright, M. C. Coniglio, J. Du, 2009: A real-time storm-scale ensemble forecast system: 2009 Spring Experiment. Preprints, 23rd Conference on Weather Analysis and Forecasting/19th Conference on Numerical Weather Prediction, Omaha, NE, USA, Amer. Meteor. Soc., CD-ROM, 16A.3. [Available from Fanyou Kong, CAPS, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Available online at ://http://ams.confex.com/ams/23WAF19NWP/techprogram/paper_154118.htm.

Krehbiel, P., W. Rison, R. Thomas, D. MacGorman, W. D. Rust, T. Marshall, M. Stolzenburg, 2006: A review of lightning phenomenology in thunderstorms. Preprints, 2nd Conference on Meteorological Applications of Lightning Data, Atlanta, GA, USA, American Meteorological Society, 6.2.

Kunkel, K. E., P. Bromirski, H. E. Brooks, T. Cavazos, A. V. Douglas, D. R. Easterling, K. A. Emanuel, P. Y. Groisman, G. J. Holland, T. R. Knutson, J. P. Kossin, P. D. Komar, D. H. Levinson, R. L. Smith, J. Allan, R. Assel, S. Changnon, J. Lawrimore, K. B. Liu, T. Peterson, 2008: Observed Changes in Weather and Climate Extremes. Weather and Climate Extremes in a Changing Climate. Regions of Focus: North America, Hawaii, Caribbean, and U.S. Pacific Islands. Synthesis and Assessment Product 3.3 Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change, T. M. Karl, G. A. Meehl, C. D. Miller, S. J. Hassol, A. M. Waple, W. L. Murray, Ed(s)., U.S. Climate Change Science Program and the Subcommittee on Glob, 35-80.

Lakshmanan, V., J. J. Gourley, Z. Flamig, S. Giagrande, 2009: A simple data-driven model for streamflow prediction. Preprints, 6th Conference on Artificial Applications to the Environmental Sciences, Phoenix, AZ, USA, Amer. Meteor. So, CD-ROM, J6.2.

Lengyel, M. M., H. E. Brooks, R. L. Holle, M. A. Cooper, 2005: Lightning casualties and their proximity to surrounding cloud-to-ground lightning. Preprints, 14th Symposium on Education, San Diego, CA, USA, American Meteorological Society, CD-ROM, P1.35.

Liang, X. Z., M. Xu, K. E. Kunkel, G. A. Grell, J. S. Kain, 2007: Regional Climate Model Simulation of U.S.–Mexico Summer Precipitation Using the Optimal Ensemble of Two Cumulus Parameterizations. Journal of Climate, 20, 5201-5207.

Marsh, P. T., H. E. Brooks, D. J. Karoly, 2007: Assessment of the severe weather environment in North America simulated by a global climate model. Atmospheric Science Letters, 8, 106.

Annual and seasonal cycles of convectively important atmospheric parameters for North America have been computed using the Community Climate System Model version 3 (CCSM3) Global Climate Model using a decade of CCSM3 data. Results for the spatial and temporal distributions of environments conducive to severe convective weather qualitatively agree with observational estimates from NCAR/NCEP global reanalyses, although the model underestimates the frequency of occurrence of severe weather environments. This result demonstrates the possibility for future studies aimed at determining possible changes in the distribution of severe weather environments associated with global climate change.

Marsh, P. T., H. E. Brooks, D. J. Karoly, 2009: Preliminary investigation into the severe thunderstorm environment of Europe simulated by the Community Climate System Model 3. Atmospheric Research, 93, 607-618.

Seasonal cycles of parameters conducive for the development of severe thunderstorms were computed using 20 years of output from the Community Climate System Model v3 (CCSM3) for both a 20th century simulation and a 21st century simulation. These parameters were compared against parameters calculated from the NCEP/NCAR Global Reanalysis data, which are of similar resolution. The CCSM3's current simulation produced seasonal and spatial distributions of both mean CAPE and favorable severe environments that were qualitatively similar to the NCEP/NCAR Global Reanalysis, although the CCSM3 underestimates the frequency of severe thunderstorm environments. Preliminary comparisons of the CCSM3's 21st century simulation under the IPCC's A2 emissions scenario to the 20th century simulation indicated a slight increase in mean CAPE in the cool season and a slight decrease in the warm season and little change in mean wind shear. However, there was a small increase in favorable severe environments for most locations resulting from an increase in the joint occurrence of high CAPE and high deep layer shear. Regions near the Mediterranean Sea experienced the biggest increase in both mean CAPE and favorable severe environments, regions near the Faeroe Islands experienced an increase in only seasonal mean CAPE, and regions across northern Europe experienced little change.

Mejia, J. F., M. Douglas, 2005: Mean structure and variability of the low-level jet across the central Gulf of California from NOAA WP-3D flight level observations during the North American Monsoon Experiment. Preprints, 6th Conference on Coastal Atmospheric and Oceanic Prediction and Processes (6COASTAL), San Diego, CA, USA, American Meteorological Society, CD-ROM, 5.8.

Mejia, J. F., M. W. Douglas, 2005: Mean structure and variability of the low-level jet across the central Gulf of California from NOAA WP-3D flight level observations during the North American Monsoon Experiment. Preprints, Sixth Conference on Coastal Atmospheric and Oceanic Prediction and Processes, San Diego, CA, USA, American Meteorological Society, 5.8.

This presentation describes lower tropospheric features over the Gulf of California, Mexico using NOAA WP-3D aircraft flight level observations made during July and August 2004 as part of the North American Monsoon Experiment (NAME). The WP-3D was flown to capture the 3-dimensional structure of the low level flow during both "strong" and "normal" monsoon flow conditions in this region. Ten flights were carried out during NAME; they were focused mainly on measuring moisture fluxes and the low-level jet (LLJ) flow along the Gulf of California. The low-level flow over the Gulf of California exhibits a low-level jet structure that is characteristic during the summertime and its stronger events appear to transport a significant amount of moisture into the southwestern United States and northwestern Mexico. We compare analyses produced by models (NCEP regional reanalysis) and the NAME sounding network observations to the aircraft measurements made on the flight days. From comparison of the aircraft data with the NAME sounding network observations we can determine how accurately the sounding network tends to estimate the actual moisture flux over the Gulf of California

Mejia, J. F., M. W. Douglas, 2005: Intensive “porpoising” with a research aircraft to determine atmospheric structure during the SALLJEX and NAME programs. Preprints, 13th Symposium on Meteorological Observations and Instrumentation, Savannah, GA, USA, American Meteorological Society, JP1.32.

Two recent field programs have focused on describing aspects of low-level jets in the Americas. Both programs have used NOAA WP-3D research aircraft to make mesoscale measurements about the jets, with the object of describing the 3-dimensional structure of the flow over relatively large areas. During both field programs the WP-3D was used as a probe, with the aircraft moving vertically while carrying out flight patterns that were mostly predetermined. The object was to describe both the horizontal structure of the jets while also describing the vertical variation of the flow. This involved trade-offs in the design of the flights. The SALLJEX flights sampled a deeper jet flow, necessitating greater vertical coverage and lesser horizontal resolution. The NAME flights were intended to sample a shallow jet that was confined in part by topography. This presentation summarizes the advantages and disadvantages of using the aircraft in a porpoising mode, with examples drawn from both experiments. The objective is to explain the benefits (and limitations) of the porpoising procedure and discuss how it may be employed most effectively.

Morss, R. E., J. K. Lazo, B. G. Brown, H. E. Brooks, P. T. Ganderton, B. N. Mills, 2008: Societal and Economic Research and Applications For Weather Forecasts: Priorities for the North American THORPEX Program. Bulletin of the American Meteorological Society, 89, 335-346.

Despite the meteorological community's long-term interest in weather–society interactions, efforts to understand socioeconomic aspects of weather prediction and to incorporate this knowledge into the weather prediction system have yet to reach critical mass. This article aims to reinvigorate interest in societal and economic research and applications (SERA) activities within the meteorological and social science communities by exploring key SERA issues and proposing SERA priorities for the next decade.

The priorities were developed by the authors, building on previous work, with input from a diverse group of social scientists and meteorologists who participated in a SERA workshop in August 2006. The workshop was organized to provide input to the North American regional component of THORPEX: A Global Atmospheric Research Programme, but the priorities identified are broadly applicable to all weather forecast research and applications.

To motivate and frame SERA activities, we first discuss the concept of high-impact weather forecasts and the chain from forecast creation to value realization. Next, we present five interconnected SERA priority themes—use of forecast information in decision making, communication of forecast uncertainty, user-relevant verification, economic value of forecasts, and decision support—and propose research integrated across the themes.

SERA activities can significantly improve understanding of weather–society interactions to the benefit of the meteorological community and society. However, reaching this potential will require dedicated effort to bring together and maintain a sustainable interdisciplinary community.

Murillo, J., M. W. Douglas, R. Orozco, J. M. Galvez, J. F. Mejia, C. Brown, 2005: Quality control of pilot balloon data for climate monitoring. Preprints, 13th Symposium on Meteorological Observations and Instrumentation, Savannah, GA, USA, American Meteorological Society, JP1.30.

Parker, D. J., M. W. Douglas, M. Christoph, A. H. Fink, S. Janicot, J. B. Ngamini, E. Afiesimama, A. Agusti-Panareda, A. Beljaars, F. Dide, A. Ddiedhiou, T. Lebel, J. Polcher, J. L. Redelsperger, C. Thorncroft, G. Wilson, 2008: The Amma radiosonde programme and its implications for the future of atmospheric monitoring over Africa.. Preprints, 28th Conference on Hurricanes and Tropical Meteorology, Orlando, FL, USA, American Meteorological Society, 3C.1.

This presentation describes the upper air observational programme which is being carried out as part of the African Monsoon Multidisciplinary Analysis (AMMA). An important goal of AMMA is to evaluate the impact of the upper-air data on weather and climate prediction for West Africa, and for the hurricane genesis regions of the tropical Atlantic. Since 2004, AMMA scientists have been working with operational agencies in Africa to reactivate silent radiosonde stations, to renovate unreliable stations, and to install new stations in regions of particular climatic importance. A comprehensive upper air network of 21 stations, including four GCOS Upper Air Network (GUAN) stations, is now active over West Africa, and during the AMMA Special Observing Period (SOP) June to September 2006 some 7000 soundings were made in the region, representing the greatest density of upper air observations ever since in the region, exceeding even the number of soundings made during the GATE programme of 1974. AMMA also encompassed a short, intensive campaign on a network of PILOT stations in the western part of the region, centered on Senegal. This activity both exposed the dilapidated state of the operational PILOT network in the region, and demonstrated that important upper air data can be collected at relatively low cost through PILOT soundings. Many operational lessons were learned in AMMA, involving technical problems in the harsh environment of sub-Saharan Africa and issues of funding, coordination and communication among the many nations and agencies involved. From these lessons we are able to make firm recommendations for the maintenance and operation of a useful upper air network in WMO Region I in the future.

Parker, D. J., A. Fink, S. Janicot, J. Ngamini, M. W. Douglas, E. Afiesimama, A. Agusti-Panareda, A. Beljaars, F. Dide, A. Diedhiou, T. Lebel, J. Polcher, J. L. Redelsperger, C. Thorncroft, G. A. Wilson, 2008: The Amma Radiosonde Program and its Implications for the Future of Atmospheric Monitoring Over Africa. Bulletin of the American Meteorological Society, 89, 1015-1027.

This article describes the upper-air program, which has been conducted as part of the African Monsoon Multidisciplinary Analysis (AMMA). Since 2004, AMMA scientists have been working in partnership with operational agencies in Africa to reactivate silent radiosonde stations, to renovate unreliable stations, and to install new stations in regions of particular climatic importance. A comprehensive upper-air network is now active over West Africa and has contributed to high-quality atmospheric monitoring over three monsoon seasons. During the period June to September 2006 high-frequency soundings were performed, in conjunction with intensive aircraft and ground-based activities: some 7,000 soundings were made, representing the greatest density of upper air measurements ever collected over the region. An important goal of AMMA is to evaluate the impact of these data on weather and climate prediction for West Africa, and for the hurricane genesis regions of the tropical Atlantic. Many operational difficulties were encountered in the program, involving technical problems in the harsh environment of sub-Saharan Africa and issues of funding, coordination, and communication among the many nations and agencies involved. In facing up to these difficulties, AMMA achieved a steady improvement in the number of soundings received by numerical weather prediction centers, with a success rate of over 88% by August 2007. From the experience of AMMA, we are therefore able to make firm recommendations for the maintenance and operation of a useful upper-air network in WMO Region I in the future.

Schwartz, C. S., J. S. Kain, S. J. Weiss, M. Xue, D. R. Bright, F. Kong, K. W. Thomas, J. J. Levit, M. C. Coniglio, 2009: Next-day convection-allowing WRF model guidance: A second look at 2 vs. 4 km grid spacing. Monthly Weather Review, 137, 3351-3372.

During the 2007 NOAA Hazardous Weather Testbed (HWT) Spring Experiment, the Center for Analysis and Prediction of Storms (CAPS) at the University of Oklahoma produced convection-allowing forecasts from a single deterministic 2 km model and a 10-member 4 km resolution ensemble. In this study, the 2 km deterministic output was compared with forecasts from the 4 km ensemble control member. Other than the difference in horizontal resolution, the two sets of forecasts featured identical WRFARW configurations, including vertical resolution, forecast domain, initial and lateral boundary conditions, and physical parameterizations. Therefore, forecast disparities were attributed solely to differences in horizontal grid spacing.

This study is a follow-up to similar work that was based on results from the 2005 Spring Experiment. Unlike the 2005 Experiment, however, model configurations were more rigorously controlled in the present study, providing a more robust dataset and a cleaner isolation of the dependence on horizontal resolution. Additionally, in this study, the 2 and 4 km output were compared to 12 km forecasts from the North American Mesoscale (NAM) model.

Model forecasts were analyzed using objective verification of mean hourly precipitation and visual comparison of individual events, primarily during the 21- to 33-hour forecast period to examine the utility of the models as next-day guidance. On average, both the 2 and 4 km model forecasts showed substantial improvement over the 12 km NAM. However, although the 2 km forecasts produced more detailed structures on the smallest resolvable scales, the patterns of convective initiation, evolution, and organization were remarkably similar to the 4 km output. Moreover, on average, metrics such as equitable threat score, frequency bias, and fractions skill score revealed no statistical improvement of the 2 km forecasts compared to the 4 km forecasts. These results, based on the 2007 dataset, corroborate previous findings, suggesting that decreasing horizontal grid spacing from 4 to 2 km provides little added value as next-day guidance for severe convective storm and heavy rain forecasters in the United States.

Schwartz, C. S., J. S. Kain, S. J. Weiss, D. R. Bright, M. Xue, F. Kong, K. W. Thomas, J. J. Levit, M. C. Coniglio, 2008: Next-day convection-allowing WRF model guidance: A second look at 2- vs. 4-km grid spacing. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor. Soc., CD-ROM, P10.3. [Available from Jack Kain, NSSL, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Available online at ://http://ams.confex.com/ams/24SLS/techprogram/paper_142052.htm.

Schwartz, C. S., J. S. Kain, D. R. Bright, S. J. Weiss, M. Xue, F. Kong, J. J. Levit, M. C. Coniglio, M. S. Wandishin, 2008: Toward improved convection-allowing ensembles: Model physics sensitivities and optimizing probabilistic guidance with small ensemble membership. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor. Soc., CD-ROM, 13A.6. [Available from Jack Kain, NSSL, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Available online at ://http://ams.confex.com/ams/24SLS/techprogram/paper_142048.htm.

Schwartz, C. S., J. S. Kain, D. R. Bright, S. J. Weiss, M. Xue, F. Kong, J. J. Levit, M. C. Coniglio, M. S. Wandishin, 2009: Optimizing probabilistic high resolution ensemble guidance for hydrologic prediction. Preprints, 23rd Conference on Hydrology, Phoenix, AZ, USA, Amer. Meteor. Soc., CD-ROM, 9.4.

Available online at ://http://ams.confex.com/ams/89annual/techprogram/paper_147171.htm.

Sobash, R. A., D. R. Bright, A. R. Dean, J. S. Kain, M. C. Coniglio, S. J. Weiss, J. J. Levit, 2008: Severe storm forecast guidance based on explicit identification of convective phenomena in WRF-model forecasts. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor. Soc., CD-ROM, 11.3.

Available online at ://http://ams.confex.com/ams/24SLS/techprogram/paper_142187.htm.

Sobash, R. A., J. S. Kain, D. R. Bright, A. R. Dean, M. C. Coniglio, S. J. Weiss, J. J. Levit, 2009: Forecast guidance for severe thunderstorms based on identification of extreme phenomena in convection-allowing model forecasts. Preprints, 23rd Conference on Weather Analysis and Forecasting/19th Conference on Numerical Weather Prediction, Omaha, NE, USA, Amer. Meteor. Soc., CD-ROM, 4B.6.

Available online at ://http://ams.confex.com/ams/23WAF19NWP/techprogram/paper_154328.htm.

Stensrud, D. J., M. C. Coniglio, R. P. Davies-Jones, J. S. Evans, 2005: Comments on “A Theory for Strong Long-Lived Squall Lines” Revisited. Journal of the Atmospheric Sciences, 62, 2989-2996.

No abstract.

Stensrud, D. J., H. E. Brooks, 2005: The future of peer review?. Weather and Forecasting, 20, 825-826.

No abstract.

Stensrud, D. J., N. Yussouf, D. C. Dowell, M. C. Coniglio, 2009: Assimilating surface data into a mesoscale model ensemble: Cold pool analyses from spring 2007. Atmos. Res., 93, 207-220.

Hourly mesoscale analyses are created through an ensemble Kalman filter assimilation of 2-m potential temperature, 2-m dewpoint temperature, and 10-m wind observations into the Weather Research and Forecast (WRF-ARW) model using the Data Assimilation Research Testbed (DART) framework. Hourly analyses are created from 1300 UTC to 0600 UTC each day from 15 March through 30 June 2007. Two cases in which a distinct isolated mesoscale convective system is seen in observations are selected for further examination. Results indicate that the ensemble mean surface analyses reproduce the surface mesoscale features associated with cold pools underneath these precipitating systems in agreement with available observations. However, the ensemble Kalman filter also is able to produce vertical motion fields and vertical structures within and above the boundary layer that are consistent with these observed surface features. In particular, a rear inflow jet is produced at roughly 1 km above ground level behind the main convective line along with an “onion” sounding along the back edge of the trailing stratiform precipitation region near a surface mesolow. Both of these structures are known to be associated with MCSs and the ability of the ensemble Kalman filter assimilation to produce these important mesoscale features is encouraging.

Stolzenburg, M., T. C. Marshall, W. D. Rust, E. Bruning, D. R. MacGorman, T. Hamlin, 2007: Electric field values observed near lightning flash initiations. Geophysical Research Letters, 34, L04804-L04804.

From a dataset of about 250 soundings of electric field (E), nine were adversely affected by lightning. These soundings are interpreted as ending near lightning initiation locations. Scaled to standard pressure, the largest observed E was 626 kV m−1 and the largest estimated E was 929 kV m−1. E exceeded runaway breakdown threshold, RBth, by factors of 1.1–3.3 before each flash, and overvoltages were 1.4–4.3. Seven cases had rapid E increases (rates of 11–100 kV m−1 s−1) in the few seconds before the flash, and in three the maximum E occurred 3 s or more before the flash. A tenth sounding with E > RBth for 38 s had subsequent lightning initiate 2 km from the balloon; one channel came within 400 m, but the flash and large E did not adversely affect the instruments. The findings suggest that E > RBth is a necessary condition for lightning initiation, but it is not sufficient.

Available online at ://http://www.agu.org/pubs/crossref/2007/2006GL028777.shtml.

Stuart, N. A., P. S. Market, B. Telfeyan, G. M. Lackmann, K. Carey, H. E. Brooks, B. C. Motta, K. Reeves, 2006: The future of humans in an increasingly automated forecast process. Bulletin of the American Meteorological Society, 87, 1-6.

The meteorological community is considering new roles for forecasters as increased accuracy in computer-generated weather forecasts continues to reduce the need for human intervention.

Available online at ://http://www.nssl.noaa.gov/users/brooks/public_html/papers/stuart.pdf.

Trapp, R. J., S. A. Tessendorf, E. S. Godfrey, H. E. Brooks, 2005: Tornadoes from Squall Lines and Bow Echoes. Part I: Climatological Distribution. Weather and Forecasting, 20, 23-34.

The primary objective of this study was to estimate the percentage of U.S. tornadoes that are spawned annually by squall lines and bow echoes, or quasi-linear convective systems (QLCSs). This was achieved by examining radar reflectivity images for every tornado event recorded during 1998-2000 in the contiguous United States. Based on these images, the type of storm associated with each tornado was classified as cell, QLCS, or other. Of the 3828 tornadoes in the database, 79% were produced by cells, 18% were produced by QLCSs, and the remaining 3% were produced by other storm types, primarily rainbands of landfallen tropical cyclones. Geographically, these percentages as well as those based on tornado days exhibited wide variations. For example, 50% of the tornado days in Indiana were associated with QLCSs. In an examination of other tornado attributes, statistically more weak (F1) and fewer strong (F2-F3) tornadoes were associated with QLCSs than with cells. QLCS tornadoes were more probable during the winter months than were cells. And finally, QLCS tornadoes displayed a comparatively higher and statistically significant tendency to occur during the late night/early morning hours. Further analysis revealed a disproportional decrease in F0-F1 events during this time of day, which led the authors to propose that many (perhaps as many as 12% of the total) weak QLCSs tornadoes were not reported.

Trapp, R. J., N. S. Diffenbaugh, H. E. Brooks, M. E. Baldwin, E. D. Robinson, J. S. Pal, 2007: Changes in severe thunderstorm environment frequency during the 21st century caused by anthropogenically enhanced global radiative forcing. Proceedings of the National Academy of Sciences of the United States of America, 104, 19723.

Severe thunderstorms comprise an extreme class of deep convective clouds and produce high-impact weather such as destructive surface winds, hail, and tornadoes. This study addresses the question of how severe thunderstorm frequency in the United States might change because of enhanced global radiative forcing associated with elevated greenhouse gas concentrations. We use global climate models and a high-resolution regional climate model to examine the larger-scale (or "environmental") meteorological conditions that foster severe thunderstorm formation. Across this model suite, we find a net increase during the late 21st century in the number of days in which these severe thunderstorm environmental conditions (NDSEV) occur. Attributed primarily to increases in atmospheric water vapor within the planetary boundary layer, the largest increases in NDSEV are shown during the summer season, in proximity to the Gulf of Mexico and Atlantic coastal regions. For example, this analysis suggests a future increase in NDSEV of 100% or more in locations such as Atlanta, GA, and New York, NY. Any direct application of these results to the frequency of actual storms also must consider the storm initiation.

Vasiloff, S. V., D. J. Seo, K. W. Howard, J. Zhang, D. H. Kitzmiller, M. G. Mullusky, W. F. Krajewski, E. A. Brandes, R. M. Rabin, D. S. Berkowitz, H. E. Brooks, J. A. McGinley, R. J. Kuligowski, B. G. Brown, 2007: Improving QPE and Very Short Term QPF: An Initiative for a Community-Wide Integrated Approach. Bulletin of the American Meteorological Society, 88, 1899-1911.

Accurate quantitative precipitation estimates (QPE) and very short term quantitative precipitation forecasts (VSTQPF) are critical to accurate monitoring and prediction of water-related hazards and water resources. While tremendous progress has been made in the last quarter-century in many areas of QPE and VSTQPF, significant gaps continue to exist in both knowledge and capabilities that are necessary to produce accurate high-resolution precipitation estimates at the national scale for a wide spectrum of users. Toward this goal, a national next-generation QPE and VSTQPF (Q2) workshop was held in Norman, Oklahoma, on 28–30 June 2005. Scientists, operational forecasters, water managers, and stakeholders from public and private sectors, including academia, presented and discussed a broad range of precipitation and forecasting topics and issues, and developed a list of science focus areas. To meet the nation's needs for the precipitation information effectively, the authors herein propose a community-wide integrated approach for precipitation information that fully capitalizes on recent advances in science and technology, and leverages the wide range of expertise and experience that exists in the research and operational communities. The concepts and recommendations from the workshop form the Q2 science plan and a suggested path to operations. Implementation of these concepts is expected to improve river forecasts and flood and flash flood watches and warnings, and to enhance various hydrologic and hydrometeorological services for a wide range of users and customers. In support of this initiative, the National Mosaic and Q2 (NMQ) system is being developed at the National Severe Storms Laboratory to serve as a community test bed for QPE and VSTQPF research and to facilitate the transition to operations of research applications. The NMQ system provides a real-time, around-the-clock data infusion and applications development and evaluation environment, and thus offers a community-wide platform for development and testing of advances in the focus areas.

Vera, C., J. Beaz, M. Douglas, C. Emmanuel, J. Marengo, J. Meitin, M. Nicolini, J. Nouges-Paegle, J. Paegle, O. Penalba, P. Salio, C. Saulo, M. A. Silva-Dias, P. Silva-Dias, E. Zipser, 2006: The South American Low-Level Jet Experiment. Bulletin of the American Meteorological Society, 87, 63-77.

Verbout, S. M., L. M. Leslie, H. E. Brooks, D. Schultz, D. Karoly, 2005: Tornado outbreaks associated with land-falling tropical cyclones in the Atlantic Basin. Preprints, 6th Conference on Coastal Atmospheric and Oceanic Prediction and Processes, San Diego, CA, USA, American Meteorological Society, CD-ROM, 7.1.

Available online at ://http://ams.confex.com/ams/Annual2005/techprogram/paper_84926.htm.

Verbout, S. M., H. E. Brooks, L. M. Leslie, D. M. Schultz, 2006: Evolution of the U.S. tornado database: 1954-2004. Weather and Forecasting, 21, 86-93.

Over the last 50 yr, the number of tornadoes reported in the United States has doubled from about 600 per year in the 1950s to around 1200 in the 2000s. This doubling is likely not related to meteorological causes alone. To account for this increase a simple least squares linear regression was fitted to the annual number of tornado reports. A "big tornado day" is a single day when numerous tornadoes and/or many tornadoes exceeding a specified intensity threshold were reported anywhere in the country. By defining a big tornado day without considering the spatial distribution of the tornadoes, a big tornado day differs from previous definitions of outbreaks. To address the increase in the number of reports, the number of reports is compared to the expected number of reports in a year based on linear regression. In addition, the F1 and greater Fujita-scale record was used in determining a big tornado day because the F1 and greater series was more stationary over time as opposed to the F2 and greater series. Thresholds were applied to the data to determine the number and intensities of the tornadoes needed to be considered a big tornado day. Possible threshold values included fractions of the annual expected value associated with the linear regression and fixed numbers for the intensity criterion. Threshold values of 1.5% of the expected annual total number of tornadoes and/or at least 8 F1 and greater tornadoes identified about 18.1 big tornado days per year. Higher thresholds such as 2.5% and/or at least 15 F1 and greater tornadoes showed similar characteristics, yet identified approximately 6.2 big tornado days per year. Finally, probability distribution curves generated using kernel density estimation revealed that big tornado days were more likely to occur slightly earlier in the year and have a narrower distribution than any given tornado day.

Available online at ://http://www.cimms.ou.edu/~schultz/pubs/verboutetal06.pdf.

Verbout, S. M., D. M. Schultz, L. M. Leslie, H. E. Brooks, D. J. Karoly, K. L. Elmore, 2007: Tornado outbreaks associated with landfalling hurricanes in the north Atlantic Basin: 1954–2004. Meteorology and Atmospheric Physics, 97, 255-271.

Tornadoes are a notable potential hazard associated with landfalling hurricanes. The purpose of this paper is to discriminate hurricanes that produce numerous tornadoes (tornado outbreaks) from those that do not (nonoutbreaks). The data consists of all hurricane landfalls that affected the United States from the North Atlantic basin from 1954 to 2004 and the United States tornado record over the same period. Because of the more than twofold increase in the number of reported tornadoes over these 51 years, a simple least-squares linear regression ("the expected number of tornadoes") was fit to the annual number of tornado reports to represent a baseline for comparison.

The hurricanes were sorted into three categories. The first category, outbreak hurricanes, was determined by hurricanes associated with the number of tornado reports exceeding a threshold of 1.5% of the annual expected number of tornadoes and at least 8 F1 and greater tornadoes during the time of landfall (from outer rainbands reaching shore to dissipation of the system). Eighteen hurricane landfalls were classified as outbreak hurricanes. Second, 37 hurricanes having less han 0.5% of the annual expected number of tornadoes were classified as nonoutbreak landfalls. Finally, 28 hurricanes that were neither outbreak nor nonoutbreak hurricanes were classified as midclass hurricane landfalls.

Stronger hurricanes are more likely to produce tornado outbreaks than weaker hurricanes. While 78% of outbreak hurricanes were category 2 or greater at landfall, only 32% of nonoutbreak hurricanes were category 2 or greater at landfall. Hurricanes that made landfall along the southern coast of the United States and recurved northeastward were more likely to produce tornadoes than those that made landfall along the east coast or those that made landfall along the southern coast but did not recurve. Recurvature was associated with a 500-hPa trough in the jet stream, which also contributed to increased deep-layer shear through the hurricane, favoring mesocyclogenesis, and increased the low-level shear, favoring tornadogenesis. The origin of the hurricane, date of landfall, and El Niño-Southern Oscillation phase do not appear to be factors in outbreak hurricane creation. The results of this study help clarify inconsistencies in the previous literature regarding tornado occurrences in landfalling hurricanes.

Available online at ://http://www.springerlink.com/content/8132257282886516/fulltext.pdf.

Ware, E. C., D. M. Schultz, H. E. Brooks, P. J. Roebber, S. L. Bruening, 2006: Improving snowfall forecasting by accounting for the climatological variability of snow density. Weather and Forecasting, 21, 94-103.

Accurately forecasting snowfall is a challenge. In particular, one poorly understood component of snowfall forecasting is determining the snow ratio. The snow ratio is the ratio of snowfall to liquid equivalent and is inversely proportional to the snow density. In a previous paper, an artificial neural network was developed to predict snow ratios probabilistically in three classes: heavy (1:1 < ratio < 9:1), average (9:1 <= ratio <= 15:1), and light (ratio > 15:1). A Web-based application for the probabilistic prediction of snow ratio in these three classes based on operational forecast model soundings and the neural network is now available. The goal of this paper is to explore the statistical characteristics of the snow ratio to determine how temperature, liquid equivalent, and wind speed can be used to provide additional guidance (quantitative, wherever possible) for forecasting snowfall, especially for extreme values of snow ratio. Snow ratio tends to increase as the low-level (surface to roughly 850 mb) temperature decreases. For example, mean low-level temperatures greater than −2.7°C rarely (less than 5% of the time) produce snow ratios greater than 25:1, whereas mean low-level temperatures less than −10.1°C rarely produce snow ratios less than 10:1. Snow ratio tends to increase strongly as the liquid equivalent decreases, leading to a nomogram for probabilistic forecasting snowfall, given a forecasted value of liquid equivalent. For example, liquid equivalent amounts 2.8–4.1 mm (0.11–0.16 in.) rarely produce snow ratios less than 14:1, and liquid equivalent amounts greater than 11.2 mm (0.44 in.) rarely produce snow ratios greater than 26:1. The surface wind speed plays a minor role by decreasing snow ratio with increasing wind speed. Although previous research has shown simple relationships to determine the snow ratio are difficult to obtain, this note helps to clarify some situations where such relationships are possible.

Available online at ://http://www.cimms.ou.edu/~schultz/pubs/wareetal06.pdf.

Watts, C. J., R. L. Scott, J. Garatuza-Payan, J. C. Rodriguez, J. H. Prueger, W. P. Kustas, M. Douglas, 2007: Changes in Vegetation Condition and Surface Fluxes during NAME 2004. Journal of Climate, 20, .

Weiss, S., J. Kain, L. Wicker, R. Davies-Jones, D. Bright, J. Levit, G. Carbin, M. Baldwin, 2005: Evaluating the skill of daily explicit predictions of mesocyclones in multiple high-resolution WRF model forecasts during the 2005 SPC/NSSL Spring Program. Preprints, 12th Conf. On Mesoscale Processes,, Albuquerque, NM, USA, Amer. Meteor. Soc., no preprint.

Weiss, S. J., J. S. Kain, D. R. Bright, J. J. Levit, M. Pyle, Z. I. Janjic, B. Ferrier, J. Du, M. L. Weisman, M. Xue, 2007: The NOAA Hazardous Weather Testbed: Collaborative testing of ensemble and convection-allowing WRF models and subsequent transfer to operations at the Storm Prediction Center.. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 6B.4.

Weiss, S. J., J. S. Kain, D. R. Bright, J. J. Levit, M. Pyle, Z. I. Janjic, B. S. Ferrier, J. Du, M. L. Weisman, M. Xue, 2007: The NOAA Hazardous Weather Testbed: Collaborative testing of ensemble and convection-allowing WRF models and subsequent transfer to operations at the Storm Prediction Center. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, Amer. Mete. [Available from S. J. Weiss, SPC, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Since 2003, the Storm Prediction Center (SPC) has played a leading role in testing various configurations of Short-Range Ensemble Forecast (SREF) systems and high resolution WRF models for their operational utility. These test and evaluation activities have occurred during organized collaborative activities in the NOAA Hazardous Weather Testbed (HWT) in Norman. The HWT is designed to bring research scientists, model developers, and forecasters together to work on issues of mutual interest, facilitating the rapid transfer of research to operations. This organizational framework helps researchers and model developers to better understand the operational challenges and requirements of forecasters, educates forecasters on new science and technological advances, and has accelerated the application of new modeling approaches to severe weather forecasting. This paper focuses on the use of the operational NCEP SREF and two experimental high resolution convection-allowing WRF models as complementary sources of information for SPC forecasters.

NCEP is running a 21 member multi-model, multi-analysis SREF system with enhanced physics diversity four times daily with output through 87 hours. SPC processes the grids from all SREF members and produces a large variety of products for severe weather forecasting, including standard spaghetti, mean and spread, probability, and max/min charts, as well as specialized multi-parameter convective fields and post-processed calibrated probabilities for the occurrence of thunderstorms, dry thunderstorms, and severe thunderstorms.

NCEP has also been running an experimental high resolution WRF-Non-hydrostatic Mesoscale Model (WRF-NMM4) for the SPC since April 2004; this model was recently upgraded to a 4 km grid length. And starting in November 2006, SPC forecasters have had access to output from a 4 km Advanced Research WRF (WRF-ARW4) developed by NCAR and run at the National Severe Storms Laboratory. Both WRF models are initialized from a cold start once daily at 0000 UTC using initial and lateral boundary conditions from the operational North American Mesoscale model, and provide forecasts through a 36 hour period over a domain covering approximately three-fourths of the U.S. Several unique WRF products have been developed for use by severe weather forecasters, including simulated reflectivity and measures of updraft rotation in model-generated storms.

The incorporation of SREF and high resolution WRF guidance into an operational severe weather forecasting environment already dealing with high volumes of observational and model data requires careful assessment of the unique strengths of each modeling system, and knowledge of the specific needs of SPC forecasters. Since the SPC severe weather forecast mission focuses on phenomena smaller than that predicted by mesoscale models, such as tornadoes and severe thunderstorms, the traditional forecast methodology has focused on first predicting the evolution of the mesoscale environment and then determining the spectrum of convective storms a particular environment may support. SREF output has been found to be particularly useful in quantifying the likelihood that the environment will occupy specific parts of convective parameter space, as well as the likelihood and timing for thunderstorms and severe thunderstorms to develop over Outlook-scale regions. While this can be extremely helpful to SPC forecasters, more detailed information about the intensity and mode of storms is also needed, since the type of severe weather (e.g., tornadoes, damaging wind) is often strongly related to convective mode. The value of the high resolution WRF guidance is most evident here, as it has capability to resolve near storm-scale convective characteristics, such as the development of discrete cells ahead of a line of storms, and the development of model storms with rotating updrafts.

We will examine the complementary role of SREF and high resolution WRF output during several strongly-forced and weakly-forced severe weather days during the winter and spring severe weather period and illustrate the operational application of these model datasets in the SPC decision-making process for both Convective Outlooks and Watches.

Available online at ://http://ams.confex.com/ams/pdfpapers/124772.pdf.

Xue, M., F. Kong, D. Weber, K. W. Thomas, Y. Wang, K. Brewster, K. K. Droegemeier, J. S. Kain, S. J. Weiss, D. R. Bright, M. S. Wandishin, M. C. Coniglio, J. Du, 2007: CAPS realtime storm-scale ensemble and high-resolution forecasts as part of the NOAA Hazardous Weather Testbed 2007 Spring Experiment.. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 3B.1.

Xue, M., F. Kong, D. B. Weber, K. W. Thomas, Y. Wang, K. Brewster, K. K. Droegemeier, J. S. Kain, S. J. Weiss, D. R. Bright, M. S. Wandishin, M. C. Coniglio, J. Du, 2007: CAPS realtime storm-scale ensemble and high-resolution forecasts as part of the NOAA Hazardous Weather Testbed 2007 Spring Experiment. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 3B.1. [Available from Ming Xue, CAPS, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

As a continuation of past collaborations with the NOAA Hazardous Weather Testbed (HWT), the Center for Analysis and Prediction of Storms (CAPS) at the University of Oklahoma will produce daily 10-member 4-km-resolution ensemble forecasts during the spring of 2007, as contributions to the HWT 2007 Spring Experiment. At the same time, a single 2-km deterministic forecast will be produced over the same domain that covers two thirds of the continental US. The forecasts will start from 2100 UTC and extend to 0600 UTC of the third day for a total length of 33 hours. The experiment will start in mid-April and last for about 2 months.

The CAPS effort in 2007 will use the WRF ARW model and the ensemble will include both initial/boundary condition and physics perturbations. The initial and boundary condition perturbations will come from the NCEP 2100 UTC SREF forecast cycle, with the control-member initial condition coming from the NAM 2100 UTC analysis on the 12 km grid. The physics perturbation members are designed for easy identification of the strengths and weakness of leading microphysics and PBL schemes within WRF.

Selected data fields will be fed directly into the NAWIPS systems in the HWT for use by experimental forecast and evaluation teams in the Spring Experiment. These will be combined with separate deterministic WRF forecasts at 3 km grid spacing, contributed by NCAR and EMC. Additional data fields from the CAPS runs will be posted on the web in realtime for external verification purposes. These include side by side comparisons of 2-km forecast composite reflectivity with the NSSL national reflectivity mosaic at 5-minute intervals and graphical displays of a large array of 2-D fields and ensemble products, including postage stamps and probability maps

Over 1000 CPUs at the Pittsburgh Supercomputing Center (PSC) will be used to produce the forecasts while additional processors at the University of Oklahoma Supercomputing Center for Education and Research (OSCER) will be used for post-processing. A special super-high-speed link capable of 200 MB/s will be set up between PSC and OSCER for data transfer.

Results of realtime forecasts and preliminary retrospective analysis on selected cases will be presented at the conference.

Available online at ://http://ams.confex.com/ams/pdfpapers/124587.pdf.

Xue, M., F. Kong, K. W. Thomas, J. Gao, Y. Wang, K. Brewster, K. K. Droegemeier, J. S. Kain, S. J. Weiss, D. R. Bright, M. C. Coniglio, J. Du, 2009: CAPS realtime 4 km multi-model convection-allowing ensemble and 1 km convection-resolving forecasts for the NOAA Hazardous Weather Testbed 2009 Spring Experiment. Preprints, 23rd Conference on Weather Analysis and Forecasting/19th Conference on Numerical Weather Prediction, Omaha, NE, USA, Amer. Meteor. Soc., CD-ROM, 16A.2.

Available online at ://http://ams.confex.com/ams/23WAF19NWP/techprogram/paper_154323.htm.

Xue, M., F. Kong, K. W. Thomas, J. Gao, Y. Wang, K. Brewster, K. K. Droegemeier, J. S. Kain, S. J. Weiss, D. R. Bright, M. C. Coniglio, J. Du, 2008: CAPS realtime storm-scale ensemble and high-resolution forecasts as part of the NOAA Hazardous Weather Testbed 2008 Spring Experiment. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor. Soc., CD-ROM, 12.2.

Available online at ://http://ams.confex.com/ams/24SLS/techprogram/paper_142036.htm.

Yu, T. Y., A. B. Chalamalasetti, R. J. Doviak, D. S. Zrnic, 2006: Resolution Enhancement Technique using Range Oversampling. Journal of Atmospheric and Oceanic Technology, 23, 228-240.

Yu, T. Y., G. Zhang, A. Chalamalasetti, R. J. Doviak, D. S. Zrnic, 2005: Improve Radar Resolution using Range Oversampling. Preprints, 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, AMS, CD-ROM, 4R.4.

Zipser, E. J., C. H. Twohy, S. C. Tsay, K. L. Thornhill, S. Tanelli, R. Ross, T. N. Krishnamurti, Q. Ji, G. Jenkins, S. Ismail, N. C. Hsu, R. Hood, G. M. Heymsfield, A. Heymsfield, J. Halvorson, H. M. Goodman, R. Ferrare, J. P. Dunion, M. Douglas, R. Cifelli, G. Chen, E. V. Browell, B. Anderson, 2009: The Saharan Air Layer and the Fate of African Easterly Waves - NASA's AMMA 2006 Field Study of Tropical Cyclogenesis. Bulletin of the American Meteorological Society, 90, 1137-1156.

In 2006, NASA led a field campaign to investigate the factors that control the fate of African easterly waves (AEWs) moving westward into the tropical Atlantic Ocean. Aircraft and surface-based equipment were based on Cape Verde's islands, helping to fill some of the data void between Africa and the Caribbean. Taking advantage of the international African Monsoon Multidisciplinary Analysis (AMMA) program over the continent, the NASA–AMMA (NAMMA) program used enhanced upstream data, whereas NOAA aircraft farther west in the Atlantic studied several of the storms downstream. Seven AEWs were studied during AMMA, with at least two becoming tropical cyclones. Some of the waves that did not develop while being sampled near Cape Verde likely intensified in the central Atlantic instead. NAMMA observations were able to distinguish between the large-scale wave structure and the smaller-scale vorticity maxima that often form within the waves. A special complication of the east Atlantic environment is the Saharan air layer (SAL), which frequently accompanies the AEWs and may introduce dry air and heavy aerosol loading into the convective storm systems in the AEWs. One of the main achievements of NAMMA was the acquisition of a database of remote sensing and in situ observations of the properties of the SAL, enabling dynamic models and satellite retrieval algorithms to be evaluated against high-quality real data. Ongoing research with this database will help determine how the SAL influences cloud micro-physics and perhaps also tropical cyclogenesis, as well as the more general question of recognizing the properties of small-scale vorticity maxima within tropical waves that are more likely to become tropical cyclones.